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Enzymes: principles and biotechnological applications


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Enzymes are biological catalysts (also known as biocatalysts) that speed up biochemical reactions in living organisms, and which can be extracted from cells and then used to catalyse a wide range of commercially important processes. This chapter covers the basic principles of enzymology, such as classification, structure, kinetics and inhibition, and also provides an overview of industrial applications. In addition, techniques for the purification of enzymes are discussed.
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Essays Biochem. (2015) 59, 1–41: doi: 10.1042/BSE0590001
Enzymes: principles and
biotechnological applications
Peter K. Robinson1
College of Science and Technology, University of Central Lancashire, Preston PR1 2HE, U.K.
Enzymes are biological catalysts (also known as biocatalysts) that speed up bio-
chemical reactions in living organisms, and which can be extracted from cells and
then used to catalyse a wide range of commercially important processes. This
chapter covers the basic principles of enzymology, such as classication, struc-
ture, kinetics and inhibition, and also provides an overview of industrial applica-
tions. In addition, techniques for the purication of enzymes are discussed.
The nature and classification of enzymes
Enzymes are biological catalysts (also known as biocatalysts) that speed up biochemical reactions
in living organisms. ey can also be extracted from cells and then used to catalyse a wide range of
commercially important processes. For example, they have important roles in the production of
sweetening agents and the modication of antibiotics, they are used in washing powders and vari-
ous cleaning products, and they play a key role in analytical devices and assays that have clinical,
forensic and environmental applications. e word ‘enzyme’ was rst used by the German physiol-
ogist Wilhelm Kühne in 1878, when he was describing the ability of yeast to produce alcohol from
sugars, and it is derived from the Greek words en (meaning ‘within’) and zume (meaning ‘yeast’).
In the late nineteenth century and early twentieth century, signicant advances were made in
the extraction, characterization and commercial exploitation of many enzymes, but it was not until
the 1920s that enzymes were crystallized, revealing that catalytic activity is associated with protein
molecules. For the next 60 years or so it was believed that all enzymes were proteins, but in the
1To whom correspondence should be addressed (email
This article is a reviewed, revised and updated version of the following ‘Biochemistry Across the School
Curriculum’ (BASC) booklet: Teal A.R. & Wymer P.E.O., 1995: Enzymes and their Role in Technology. For further
information and to provide feedback on this or any other Biochemical Society education resource, please contact For further information on other Biochemical Society publications, please visit www.
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1980s it was found that some ribonucleic acid (RNA) molecules are also able to exert catalytic
eects. ese RNAs, which are called ribozymes, play an important role in gene expression. In the
same decade, biochemists also developed the technology to generate antibodies that possess cata-
lytic properties. ese so-called ‘abzymes’ have signicant potential both as novel industrial cata-
lysts and in therapeutics. Notwithstanding these notable exceptions, much of classical enzymology,
and the remainder of this essay, is focused on the proteins that possess catalytic activity.
As catalysts, enzymes are only required in very low concentrations, and they speed up
reactions without themselves being consumed during the reaction. We usually describe
enzymes as being capable of catalysing the conversion of substrate molecules into product
molecules as follows:
Enzymes are potent catalysts
e enormous catalytic activity of enzymes can perhaps best be expressed by a constant, kcat, that
is variously referred to as the turnover rate, turnover frequency or turnover number. is con-
stant represents the number of substrate molecules that can be converted to product by a single
enzyme molecule per unit time (usually per minute or per second). Examples of turnover rate
values are listed in Table 1. For example, a single molecule of carbonic anhydrase can catalyse the
conversion of over half a million molecules of its substrates, carbon dioxide (CO2) and water
(H2O), into the product, bicarbonate (HCO3), every second—a truly remarkable achievement.
Enzymes are specific catalysts
As well as being highly potent catalysts, enzymes also possess remarkable specicity in that
they generally catalyse the conversion of only one type (or at most a range of similar types) of
substrate molecule into product molecules.
Some enzymes demonstrate group specicity. For example, alkaline phosphatase (an
enzyme that is commonly encountered in rst-year laboratory sessions on enzyme kinetics)
can remove a phosphate group from a variety of substrates.
Other enzymes demonstrate much higher specicity, which is described as absolute speci-
city. For example, glucose oxidase shows almost total specicity for its substrate, β-D-glucose,
and virtually no activity with any other monosaccharides. As we shall see later, this specicity
is of paramount importance in many analytical assays and devices (biosensors) that measure a
specic substrate (e.g. glucose) in a complex mixture (e.g. a blood or urine sample).
Table 1. Turnover rate of some common enzymes showing wide variation.
Enzyme Turnover rate (mole product s1 mole enzyme1)
Carbonic anhydrase 600 000
Catalase 93 000
β–galactosidase 200
Chymotrypsin 100
Tyrosinase 1
P.K. Robinson 3
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Enzyme names and classification
Enzymes typically have common names (oen called ‘trivial names’) which refer to the reaction
that they catalyse, with the sux -ase (e.g. oxidase, dehydrogenase, carboxylase), although individ-
ual proteolytic enzymes generally have the sux -in (e.g. trypsin, chymotrypsin, papain). Oen
the trivial name also indicates the substrate on which the enzyme acts (e.g. glucose oxidase, alco-
hol dehydrogenase, pyruvate decarboxylase). However, some trivial names (e.g. invertase, diastase,
catalase) provide little information about the substrate, the product or the reaction involved.
Due to the growing complexity of and inconsistency in the naming of enzymes, the
International Union of Biochemistry set up the Enzyme Commission to address this issue. e rst
Enzyme Commission Report was published in 1961, and provided a systematic approach to the
naming of enzymes. e sixth edition, published in 1992, contained details of nearly 3 200 dierent
enzymes, and supplements published annually have now extended this number to over 5 000.
Within this system, all enzymes are described by a four-part Enzyme Commission (EC)
number. For example, the enzyme with the trivial name lactate dehydrogenase has the EC
number, and is more correctly called –lactate: NAD+ oxidoreductase.
e rst part of the EC number refers to the reaction that the enzyme catalyses (Table 2).
e remaining digits have dierent meanings according to the nature of the reaction identied
by the rst digit. For example, within the oxidoreductase category, the second digit denotes the
hydrogen donor (Table 3) and the third digit denotes the hydrogen acceptor (Table 4).
us lactate dehydrogenase with the EC number is an oxidoreductase (indicated
by the rst digit) with the alcohol group of the lactate molecule as the hydrogen donor (second
digit) and NAD+ as the hydrogen acceptor (third digit), and is the 27th enzyme to be catego-
rized within this group (fourth digit).
Table 2. Enzyme Classification: Main classes of enzymes in EC system.
First EC digit Enzyme class Reaction type
1. Oxidoreductases Oxidation/reduction
2. Transferases Atom/group transfer (excluding other classes)
3. Hydrolases Hydrolysis
4. Lyases Group removal (excluding 3.)
5. Isomerases Isomerization
6. Ligases Joining of molecules linked to the breakage of
a pyrophosphate bond
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Fortunately, it is now very easy to nd this information for any individual enzyme using
the Enzyme Nomenclature Database (available at
Enzyme structure and substrate binding
Amino acid-based enzymes are globular proteins that range in size from less than 100 to more
than 2 000 amino acid residues. ese amino acids can be arranged as one or more polypep-
tide chains that are folded and bent to form a specic three-dimensional structure, incorporat-
ing a small area known as the active site (Figure 1), where the substrate actually binds. e
active site may well involve only a small number (less than 10) of the constituent amino acids.
It is the shape and charge properties of the active site that enable it to bind to a single type
of substrate molecule, so that the enzyme is able to demonstrate considerable specicity in its
catalytic activity.
e hypothesis that enzyme specicity results from the complementary nature of the sub-
strate and its active site was rst proposed by the German chemist Emil Fischer in 1894, and
became known as Fischer’s ‘lock and key hypothesis’, whereby only a key of the correct size and
shape (the substrate) ts into the keyhole (the active site) of the lock (the enzyme). It is
astounding that this theory was proposed at a time when it was not even established that
Table 3. Enzyme Classification: Secondary classes of oxidoreductase enzymes
in EC system.
second EC digit
Hydrogen or electron donor
1. Alcohol (CHOH)
2. Aldehyde or ketone (CO)
4. Primary amine (CHNH2 or CHNH3
5. Secondary amine (CHNH)
6. NADH or NADPH (when another redox catalyst is the acceptor)
Table 4. Enzyme Classification: Tertiary classes of oxidoreductase enzymes in
EC system.
Oxidoreductases: third EC digit Hydrogen or electron acceptor
1. NAD+ or NADP+
2. Fe3+ (e.g. cytochromes)
3. O2
4. Other
P.K. Robinson 5
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enzymes were proteins. As more was learned about enzyme structure through techniques such
as X-ray crystallography, it became clear that enzymes are not rigid structures, but are in fact
quite exible in shape. In the light of this nding, in 1958 Daniel Koshland extended Fischers
ideas and presented the ‘induced-t model’ of substrate and enzyme binding, in which the
enzyme molecule changes its shape slightly to accommodate the binding of the substrate. e
analogy that is commonly used is the ‘hand-in-glove model, where the hand and glove are
broadly complementary in shape, but the glove is moulded around the hand as it is inserted in
order to provide a perfect match.
Since it is the active site alone that binds to the substrate, it is logical to ask what is the
role of the rest of the protein molecule. e simple answer is that it acts to stabilize the
active site and provide an appropriate environment for interaction of the site with the sub-
strate molecule. erefore the active site cannot be separated out from the rest of the protein
without loss of catalytic activity, although laboratory-based directed (or forced) evolution
studies have shown that it is sometimes possible to generate smaller enzymes that do retain
It should be noted that although a large number of enzymes consist solely of protein,
many also contain a non-protein component, known as a cofactor, that is necessary for the
enzyme’s catalytic activity. A cofactor may be another organic molecule, in which case it is
called a coenzyme, or it may be an inorganic molecule, typically a metal ion such as iron, man-
ganese, cobalt, copper or zinc. A coenzyme that binds tightly and permanently to the protein is
generally referred to as the prosthetic group of the enzyme.
When an enzyme requires a cofactor for its activity, the inactive protein component is
generally referred to as an apoenzyme, and the apoenzyme plus the cofactor (i.e. the active
enzyme) is called a holoenzyme (Figure 2).
e need for minerals and vitamins in the human diet is partly attributable to their roles
within metabolism as cofactors and coenzymes.
Enzymes and reaction equilibrium
How do enzymes work? e broad answer to this question is that they do not alter the equilib-
rium (i.e. the thermodynamics) of a reaction. is is because enzymes do not fundamentally
change the structure and energetics of the products and reagents, but rather they simply allow
Figure 1. Representation of substrate binding to the active site of an enzyme
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the reaction equilibrium to be attained more rapidly. Let us therefore begin by clarifying the
concept of chemical equilibrium.
In many cases the equilibrium of a reaction is far ‘to the right’—that is, virtually all of the
substrate (S) is converted into product (P). For this reason, reactions are oen written as
is is a simplication, as in all cases it is more correct to write this reaction as follows:
is indicates the presence of an equilibrium. To understand this concept it is perhaps
most helpful to look at a reaction where the equilibrium point is quite central.
For example:
Glucose isomerase
In this reaction, if we start with a solution of 1 mol l1 glucose and add the enzyme, then
upon completion we will have a mixture of approximately 0.5 mol l1 glucose and 0.5 mol l1
fructose. is is the equilibrium point of this particular reaction, and although it may only
take a couple of seconds to reach this end point with the enzyme present, we would in fact
come to the same point if we put glucose into solution and waited many months for the reac-
tion to occur in the absence of the enzyme. Interestingly, we could also have started this reac-
tion with a 1 mol l1 fructose solution, and it would have proceeded in the opposite direction
until the same equilibrium point had been reached.
e equilibrium point for this reaction is expressed by the equilibrium constant Keq as
Substrate concentration at end point
Substrate concentr
=aation at end point
05 1
Figure 2. The components of a holoenzyme.
P.K. Robinson 7
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us for a reaction with central equilibrium, Keq = 1, for an equilibrium ‘to the right’ Keq
is >1, and for an equilibrium ‘to the leKeq is <1.
erefore if a reaction has a Keq value of 106, the equilibrium is very far to the right and
can be simplied by denoting it as a single arrow. We may oen describe this type of reaction
as ‘going to completion. Conversely, if a reaction has a Keq value of 106, the equilibrium is very
far to the le, and for all practical purposes it would not really be considered to proceed at all.
It should be noted that although the concentration of reactants has no eect on the equi-
librium point, environmental factors such as pH and temperature can and do aect the posi-
tion of the equilibrium.
It should also be noted that any biochemical reaction which occurs in vivo in a living sys-
tem does not occur in isolation, but as part of a metabolic pathway, which makes it more di-
cult to conceptualize the relationship between reactants and reactions. In vivo reactions are not
allowed to proceed to their equilibrium position. If they did, the reaction would essentially
stop (i.e. the forward and reverse reactions would balance each other), and there would be no
net ux through the pathway. However, in many complex biochemical pathways some of the
individual reaction steps are close to equilibrium, whereas others are far from equilibrium, the
latter (catalysed by regulatory enzymes) having the greatest capacity to control the overall ux
of materials through the pathway.
Enzymes form complexes with their substrates
We oen describe an enzyme-catalysed reaction as proceeding through three stages as follows:
ES ES complex EP+→ +
e ES complex represents a position where the substrate (S) is bound to the enzyme (E)
such that the reaction (whatever it might be) is made more favourable. As soon as the reaction
has occurred, the product molecule (P) dissociates from the enzyme, which is then free to bind
to another substrate molecule. At some point during this process the substrate is converted
into an intermediate form (oen called the transition state) and then into the product.
e exact mechanism whereby the enzyme acts to increase the rate of the reaction diers
from one system to another. However, the general principle is that by binding of the substrate
to the enzyme, the reaction involving the substrate is made more favourable by lowering the
activation energy of the reaction.
In terms of energetics, reactions can be either exergonic (releasing energy) or endergonic
(consuming energy). However, even in an exergonic reaction a small amount of energy,
termed the activation energy, is needed to give the reaction a ‘kick start.’ A good analogy is that
of a match, the head of which contains a mixture of energy-rich chemicals (phosphorus ses-
quisulde and potassium chlorate). When a match burns it releases substantial amounts of
light and heat energy (exergonically reacting with O2 in the air). However, and perhaps fortu-
nately, a match will not spontaneously ignite, but rather a small input of energy in the form of
heat generated through friction (i.e. striking of the match) is needed to initiate the reaction. Of
course once the match has been struck the amount of energy released is considerable, and
greatly exceeds the small energy input during the striking process.
As shown in Figure 3, enzymes are considered to lower the activation energy of a system
by making it energetically easier for the transition state to form. In the presence of an enzyme
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catalyst, the formation of the transition state is energetically more favourable (i.e. it requires
less energy for the ‘kick start’), thereby accelerating the rate at which the reaction will proceed,
but not fundamentally changing the energy levels of either the reactant or the product.
Properties and mechanisms of enzyme
Enzyme kinetics
Enzyme kinetics is the study of factors that determine the speed of enzyme-catalysed reac-
tions. It utilizes some mathematical equations that can be confusing to students when they rst
encounter them. However, the theory of kinetics is both logical and simple, and it is essential
to develop an understanding of this subject in order to be able to appreciate the role of
enzymes both in metabolism and in biotechnology.
Assays (measurements) of enzyme activity can be performed in either a discontinuous or
continuous fashion. Discontinuous methods involve mixing the substrate and enzyme together
and measuring the product formed aer a set period of time, so these methods are generally easy
and quick to perform. In general we would use such discontinuous assays when we know little
about the system (and are making preliminary investigations), or alternatively when we know a
great deal about the system and are certain that the time interval we are choosing is appropriate.
In continuous enzyme assays we would generally study the rate of an enzyme-catalysed
reaction by mixing the enzyme with the substrate and continuously measuring the appear-
ance of product over time. Of course we could equally well measure the rate of the reaction
by measuring the disappearance of substrate over time. Apart from the actual direction (one
increasing and one decreasing), the two values would be identical. In enzyme kinetics experi-
ments, for convenience we very oen use an articial substrate called a chromogen that yields
Figure 3. Effect of an enzyme on reducing the activation energy required to start a
reaction where (a) is uncatalysed and (b) is enzyme-catalysed reaction.
P.K. Robinson 9
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a brightly coloured product, making the reaction easy to follow using a colorimeter or a spec-
trophotometer. However, we could in fact use any available analytical equipment that has the
capacity to measure the concentration of either the product or the substrate.
In almost all cases we would also add a buer solution to the mixture. As we shall see,
enzyme activity is strongly inuenced by pH, so it is important to set the pH at a specic value
and keep it constant throughout the experiment.
Our rst enzyme kinetics experiment may therefore involve mixing a substrate solution
(chromogen) with a buer solution and adding the enzyme. is mixture would then be
placed in a spectrophotometer and the appearance of the coloured product would be meas-
ured. is would enable us to follow a rapid reaction which, aer a few seconds or minutes,
might start to slow down, as shown in Figure 4.
A common reason for this slowing down of the speed (rate) of the reaction is that the
substrate within the mixture is being used up and thus becoming limiting. Alternatively, it may
be that the enzyme is unstable and is denaturing over the course of the experiment, or it could
be that the pH of the mixture is changing, as many reactions either consume or release pro-
tons. For these reasons, when we are asked to specify the rate of a reaction we do so early on,
as soon as the enzyme has been added, and when none of the above-mentioned limitations
Figure 4. Formation of product in an enzyme-catalysed reaction, plotted against time.
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apply. We refer to this initial rapid rate as the initial velocity (v0). Measurement of the reaction
rate at this early stage is also quite straightforward, as the rate is eectively linear, so we can
simply draw a straight line and measure the gradient (by dividing the concentration change by
the time interval) in order to evaluate the reaction rate over this period.
We may now perform a range of similar enzyme assays to evaluate how the initial velocity
changes when the substrate or enzyme concentration is altered, or when the pH is changed.
ese studies will help us to characterize the properties of the enzyme under study.
e relationship between enzyme concentration and the rate of the reaction is usually a
simple one. If we repeat the experiment just described, but add 10% more enzyme, the reaction
will be 10% faster, and if we double the enzyme concentration the reaction will proceed twice
as fast. us there is a simple linear relationship between the reaction rate and the amount of
enzyme available to catalyse the reaction (Figure 5).
This relationship applies both to enzymes in vivo and to those used in biotechnologi-
cal applications, where regulation of the amount of enzyme present may control reaction
When we perform a series of enzyme assays using the same enzyme concentration,
but with a range of different substrate concentrations, a slightly more complex relation-
ship emerges, as shown in Figure 6. Initially, when the substrate concentration is
increased, the rate of reaction increases considerably. However, as the substrate concentra-
tion is increased further the effects on the reaction rate start to decline, until a stage is
reached where increasing the substrate concentration has little further effect on the reac-
tion rate. At this point the enzyme is considered to be coming close to saturation with
substrate, and demonstrating its maximal velocity (Vmax). Note that this maximal velocity
is in fact a theoretical limit that will not be truly achieved in any experiment, although we
might come very close to it.
Figure 5. Relationship between enzyme concentration and the rate of an enzyme-
catalysed reaction.
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e relationship described here is a fairly common one, which a mathematician would
immediately identify as a rectangular hyperbola. e equation that describes such a relation-
ship is as follows:
e two constants a and b thus allow us to describe this hyperbolic relationship, just as
with a linear relationship (y = mx + c), which can be expressed by the two constants m (the
slope) and c (the intercept).
We have in fact already dened the constant a — it is Vmax. e constant b is a little more
complex, as it is the value on the x-axis that gives half of the maximal value of y. In enzymol-
ogy we refer to this as the Michaelis constant (Km), which is dened as the substrate concentra-
tion that gives half-maximal velocity.
Our nal equation, usually called the Michaelis–Menten equation, therefore becomes:
Initial rate of reaction ( )= Substrate concentration
SSubstrate concentration
In 1913, Leonor Michaelis and Maud Menten rst showed that it was in fact possible to
derive this equation mathematically from rst principles, with some simple assumptions about
the way in which an enzyme reacts with a substrate to form a product. Central to their deriva-
tion is the concept that the reaction takes place via the formation of an ES complex which,
once formed, can either dissociate (productively) to release product, or else dissociate in the
reverse direction without any formation of product. us the reaction can be represented as
follows, with k1, k1 and k2 being the rate constants of the three individual reaction steps:
 ES
Figure 6. Relationship between substrate concentration and the rate of an enzyme-
catalysed reaction.
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e Michaelis–Menten derivation requires two important assumptions. e rst assump-
tion is that we are considering the initial velocity of the reaction (v0), when the product con-
centration will be negligibly small (i.e. [S] [P]), such that we can ignore the possibility of
any product reverting to substrate. e second assumption is that the concentration of sub-
strate greatly exceeds the concentration of enzyme (i.e. [S] [E]).
The derivation begins with an equation for the expression of the initial rate, the rate
of formation of product, as the rate at which the ES complex dissociates to form product.
This is based upon the rate constant k2 and the concentration of the ES complex, as
[] (1)
Since ES is an intermediate, its concentration is unknown, but we can express it in terms
of known values. In a steady-state approximation we can assume that although the concentra-
tion of substrate and product changes, the concentration of the ES complex itself remains con-
stant. e rate of formation of the ES complex and the rate of its breakdown must therefore
balance, where:
Rate of ES complex formation E
Rate of ES complex breakdown ES
Hence, at steady state:
is equation can be rearranged to yield [ES] as follows:
[] [][S]
e Michaelis constant Km can be dened as follows:
Equation 2 may thus be simplied to:
[] []
=K (3)
Since the concentration of substrate greatly exceeds the concentration of enzyme (i.e.
[S][E]), the concentration of uncombined substrate [S] is almost equal to the total concen-
tration of substrate. e concentration of uncombined enzyme [E] is equal to the total enzyme
P.K. Robinson 13
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concentration [E]T minus that combined with substrate [ES]. Introducing these terms to
Equation 3 and solving for ES gives us the following:
We can then introduce this term into Equation 1 to give:
vk K
[] []
e term k2[E]T in fact represents Vmax, the maximal velocity. us Michaelis and Menten
were able to derive their nal equation as:
A more detailed derivation of the Michaelis–Menten equation can be found in many bio-
chemistry textbooks (see section 4 of Recommended Reading section). ere are also some very
helpful web-based tutorials available on the subject.
Michaelis constants have been determined for many commonly used enzymes, and are
typically in the lower millimolar range (Table 5).
It should be noted that enzymes which catalyse the same reaction, but which are derived
from dierent organisms, can have widely diering Km values. Furthermore, an enzyme with
multiple substrates can have quite dierent Km values for each substrate.
A low Km value indicates that the enzyme requires only a small amount of substrate in
order to become saturated. erefore the maximum velocity is reached at relatively low sub-
strate concentrations. A high Km value indicates the need for high substrate concentrations in
order to achieve maximum reaction velocity. us we generally refer to Km as a measure of the
anity of the enzyme for its substrate—in fact it is an inverse measure, where a high Km indi-
cates a low anity, and vice versa.
e Km value tells us several important things about a particular enzyme.
Table 5. Typical range of values of the Michaelis constant.
Enzyme Km (mmol l1)
Carbonic anhydrase 26
Chymotrypsin 15
Ribonuclease 8
Tyrosyl-tRNA synthetase 0.9
Pepsin 0.3
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1. An enzyme with a low Km value relative to the physiological concentration of substrate will
probably always be saturated with substrate, and will therefore act at a constant rate,
regardless of variations in the concentration of substrate within the physiological range.
2. An enzyme with a high Km value relative to the physiological concentration of substrate will
not be saturated with substrate, and its activity will therefore vary according to the concen-
tration of substrate, so the rate of formation of product will depend on the availability of
3. If an enzyme acts on several substrates, the substrate with the lowest Km value is fre-
quently assumed to be that enzyme’s ‘natural’ substrate, although this may not be true in
all cases.
4. If two enzymes (with similar Vmax) in dierent metabolic pathways compete for the same
substrate, then if we know the Km values for the two enzymes we can predict the relative
activity of the two pathways. Essentially the pathway that has the enzyme with the lower Km
value is likely to be the ‘preferred pathway’, and more substrate will ow through that path-
way under most conditions. For example, phosphofructokinase (PFK) is the enzyme that
catalyses the rst committed step in the glycolytic pathway, which generates energy in the
form of ATP for the cell, whereas glucose-1-phosphate uridylyltransferase (GUT) is an
enzyme early in the pathway leading to the synthesis of glycogen (an energy storage mole-
cule). Both enzymes use hexose monophosphates as substrates, but the Km of PFK for its
substrate is lower than that of GUT for its substrate. us at lower cellular hexose phos-
phate concentrations, PFK will be active and GUT will be largely inactive. At higher hexose
phosphate concentrations both pathways will be active. is means that the cells only store
glycogen in times of plenty, and always give preference to the pathway of ATP production,
which is the more essential function.
Very oen it is not possible to estimate Km values from a direct plot of velocity against
substrate concentration (as shown in Figure 6) because we have not used high enough
Figure 7. (a) Direct plot. (b) Lineweaver–Burk plot of the same kinetic data.
P.K. Robinson 15
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substrate concentrations to come even close to estimating maximal velocity, and therefore we
cannot evaluate half-maximal velocity and thus Km. Fortunately, we can plot our experimental
data in a slightly dierent way in order to obtain these values. e most commonly used
alternative is the Lineweaver–Burk plot (oen called the double-reciprocal plot). is plot
linearizes the hyperbolic curved relationship, and the line produced is easy to extrapolate,
allowing evaluation of Vmax and Km. For example, if we obtained only the rst seven data
points in Figure 6, we would have diculty estimating Vmax from a direct plot as shown in
Figure 7a.
However, as shown in Figure 7b, if these seven points are plotted on a graph of 1/velocity
against 1/substrate concentration (i.e. a double-reciprocal plot), the data are linearized, and the
line can be easily extrapolated to the le to provide intercepts on both the y-axis and the
x-axis, from which Vmax and Km, respectively, can be evaluated.
One signicant practical drawback of using the Lineweaver–Burk plot is the excessive
inuence that it gives to measurements made at the lowest substrate concentrations. ese
concentrations might well be the most prone to error (due to diculties in making multiple
dilutions), and result in reaction rates that, because they are slow, might also be most prone to
measurement error. Often, as shown in Figure 8, such points when transformed on the
Lineweaver–Burk plot have a signicant impact on the line of best t estimated from the data,
and therefore on the extrapolated values of both Vmax and Km. e two sets of points shown in
Figure 8 are identical except for the single point at the top right, which reects (because of the
plot’s double-reciprocal nature) a single point derived from a very low substrate concentration
and a low reaction rate. However, this single point can have an enormous impact on the line of
best t and the accompanying estimates of kinetic constants.
In fact there are other kinetic plots that can be used, including the Eadie–Hofstee plot,
the Hanes plot and the Eisenthal–Cornish-Bowden plot, which are less prone to such prob-
lems. However, the Lineweaver–Burk plot is still the most commonly described kinetic plot in
the majority of enzymology textbooks, and thus retains its influence in undergraduate
Figure 8. Lineweaver–Burk plot of similar kinetic data, which differ only in a single.
(Final data point (a) 1/v 0.03 at 1/S of 0.2 and (b) 1/v 0.031 at 1/S of 0.18).
16 Essays in Biochemistry volume 59 2015
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Enzymes are affected by pH and temperature
Various environmental factors are able to aect the rate of enzyme-catalysed reactions through
reversible or irreversible changes in the protein structure. e eects of pH and temperature
are generally well understood.
Most enzymes have a characteristic optimum pH at which the velocity of the catalysed
reaction is maximal, and above and below which the velocity declines (Figure 9).
e pH prole is dependent on a number of factors. As the pH changes, the ionization of
groups both at the enzyme’s active site and on the substrate can alter, inuencing the rate of
binding of the substrate to the active site. ese eects are oen reversible. For example, if we
take an enzyme with an optimal pH (pHopt) of 7.0 and place it in an environment at pH 6.0 or
8.0, the charge properties of the enzyme and the substrate may be suboptimal, such that bind-
ing and hence the reaction rate are lowered. If we then readjust the pH to 7.0, the optimal
charge properties and hence the maximal activity of the enzyme are oen restored. However, if
we place the enzyme in a more extreme acidic or alkaline environment (e.g. at pH 1 or 14),
although these conditions may not actually lead to changes in the very stable covalent struc-
ture of the protein (i.e. its conguration), they may well produce changes in the conformation
(shape) of the protein such that, when it is returned to pH 7.0, the original conformation and
hence the enzyme’s full catalytic activity are not restored.
It should be noted that the optimum pH of an enzyme may not be identical to that of its
normal intracellular surroundings. is indicates that the local pH can exert a controlling
inuence on enzyme activity.
e eects of temperature on enzyme activity are quite complex, and can be regarded as
two forces acting simultaneously but in opposite directions. As the temperature is raised, the
rate of molecular movement and hence the rate of reaction increases, but at the same time
there is a progressive inactivation caused by denaturation of the enzyme protein. is becomes
more pronounced as the temperature increases, so that an apparent temperature optimum
(Topt) is observed (Figure 10).
Figure 9. The pH profile of β-glucosidase.
P.K. Robinson 17
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ermal denaturation is time dependent, and for an enzyme the term ‘optimum tempera-
ture’ has little real meaning unless the duration of exposure to that temperature is recorded.
e thermal stability of an enzyme can be determined by rst exposing the protein to a range
of temperatures for a xed period of time, and subsequently measuring its activity at one
favourable temperature (e.g. 25°C).
e temperature at which denaturation becomes important varies from one enzyme to
another. Normally it is negligible below 30°C, and starts to become appreciable above 40°C.
Typically, enzymes derived from microbial sources show much higher thermal stability than
do those from mammalian sources, and enzymes derived from extremely thermophilic micro-
organisms, such as thermolysin (a protease from Bacillus thermoproteolyticus) and Taq poly-
merase (a DNA polymerase from ermus aquaticus), might be completely thermostable at
70°C and still retain substantial levels of activity even at 100°C.
Enzymes are sensitive to inhibitors
Substances that reduce the activity of an enzyme-catalysed reaction are known as inhibitors.
ey act by either directly or indirectly inuencing the catalytic properties of the active site.
Inhibitors can be foreign to the cell or natural components of it. ose in the latter category
can represent an important element of the regulation of cell metabolism. Many toxins and also
many pharmacologically active agents (both illegal drugs and prescription and over-the-
counter medicines) act by inhibiting specic enzyme-catalysed processes.
Reversible inhibition
Inhibitors are classied as reversible inhibitors when they bind reversibly to an enzyme. A
molecule that is structurally similar to the normal substrate may be able to bind reversibly to
the enzyme’s active site and therefore act as a competitive inhibitor. For example, malonate is a
competitive inhibitor of the enzyme succinate dehydrogenase, as it is capable of binding to the
enzyme’s active site due to its close structural similarity to the enzyme’s natural substrate, suc-
cinate (see below). When malonate occupies the active site of succinate dehydrogenase it
Figure 10. The effect of temperature on enzyme activity.
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prevents the natural substrate, succinate, from binding, thereby slowing down the rate of oxi-
dation of succinate to fumarate (i.e. inhibiting the reaction).
One of the characteristics of competitive inhibitors is that they can be displaced from the
active site if high concentrations of substrate are used, thereby restoring enzyme activity. us
competitive inhibitors increase the Km of a reaction because they increase the concentration of
substrate required to saturate the enzyme. However, they do not change Vmax itself.
In the case of certain enzymes, high concentrations of either the substrate or the product
can be inhibitory. For example, invertase activity is considerably reduced in the presence of
high concentrations of sucrose (its substrate), whereas the β-galactosidase of Aspergillus niger
is strongly inhibited by galactose (its product). Products of an enzyme reaction are some of the
most commonly encountered competitive inhibitors.
Other types of reversible inhibitor also exist. Non-competitive inhibitors react with the
enzyme at a site distinct from the active site. erefore the binding of the inhibitor does not
physically block the substrate–binding site, but it does prevent subsequent reaction. Most non-
competitive inhibitors are chemically unrelated to the substrate, and their inhibition cannot be
overcome by increasing the substrate concentration. Such inhibitors in eect reduce the con-
centration of the active enzyme in solution, thereby reducing the Vmax of the reaction.
However, they do not change the value of Km.
Uncompetitive inhibition is rather rare, occurring when the inhibitor is only able to bind
to the enzyme once a substrate molecule has itself bound. As such, inhibition is most signi-
cant at high substrate concentrations, and results in a reduction in the Vmax of the reaction.
Uncompetitive inhibition also causes a reduction in Km, which seems somewhat counterintui-
tive as this means that the anity of the enzyme for its substrate is actually increased when the
inhibitor is present. is eect occurs because the binding of the inhibitor to the ES complex
eectively removes ES complex and thereby aects the overall equilibrium of the reaction
favouring ES complex formation. It is noteworthy however that since both Vmax and Km are
P.K. Robinson 19
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reduced the observed reaction rates with inhibitor present are always lower than those in the
absence of the uncompetitive inhibitor.
Irreversible inhibitors and poisons
If an inhibitor binds permanently to an enzyme it is known as an irreversible inhibitor. Many
irreversible inhibitors are therefore potent toxins.
Organophosphorus compounds such as diisopropyl uorophosphate (DFP) inhibit ace-
tylcholinesterase activity by reacting covalently with an important serine residue found within
the active site of the enzyme. e physiological eect of this inactivation is interference with
neurotransmitter inactivation at the synapses of nerves, resulting in the constant propagation
of nerve impulses, which can lead to death. DFP was originally evaluated by the British as a
chemical warfare agent during World War Two, and modied versions of this compound are
now widely used as organophosphate pesticides (e.g. parathione, malathione).
Allosteric regulators and the control of enzyme activity
Having spent time learning about enzyme kinetics and the Michaelis–Menten relationship, it is
oen quite disconcerting to nd that some of the most important enzymes do not in fact display
such properties. Allosteric enzymes are key regulatory enzymes that control the activities of met-
abolic pathways by responding to inhibitors and activators. ese enzymes in fact show a sigmoi-
dal (S-shaped) relationship between reaction rate and substrate concentration (Figure11), rather
than the usual hyperbolic relationship. us for allosteric enzymes there is an area where activity
is lower than that of an equivalent ‘normal’ enzyme, and also an area where activity is higher than
that of an equivalent ‘normal’ enzyme, with a rapid transition between these two phases. is is
rather like a switch that can quickly be changed from ‘o ’ (low activity) to ‘on’ (full activity).
Most allosteric enzymes are polymeric—that is, they are composed of at least two (and
oen many more) individual polypeptide chains. ey also have multiple active sites where the
substrate can bind. Much of our understanding of the function of allosteric enzymes comes
Figure 11. Activity/substrate profiles of allosteric () and non-allosteric () enzymes
with the same affinity and maximal velocity.
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from studies of haemoglobin which, although it is not an enzyme, binds oxygen in a similarly
co-operative way and thus also demonstrates this sigmoidal relationship. Allosteric enzymes
have an initially low anity for the substrate, but when a single substrate molecule binds, this
may break some bonds within the enzyme and thereby change the shape of the protein such
that the remaining active sites are able to bind with a higher affinity. Therefore allosteric
enzymes are oen described as moving from a tensed state or T-state (low anity) in which no
substrate is bound, to a relaxed state or R-state (high anity) as substrate binds. Other mole-
cules can also bind to allosteric enzymes, at additional regulatory sites (i.e. not at the active site).
Molecules that stabilize the protein in its T-state therefore act as allosteric inhibitors, whereas
molecules that move the protein to its R-state will act as allosteric activators or promoters.
A good example of an allosteric enzyme is aspartate transcarbamoylase (ATCase), a key
regulatory enzyme that catalyses the rst committed step in the sequence of reactions that pro-
duce the pyrimidine nucleotides which are essential components of DNA and RNA. e reac-
tion is as follows:
e end product in the pathway, the pyrimidine nucleotide cytidine triphosphate (CTP), is
an active allosteric inhibitor of the enzyme ATCase. erefore when there is a high concentra-
tion of CTP in the cell, this feeds back and inhibits the ATCase enzyme, reducing its activity
and thus lowering the rate of production of further pyrimidine nucleotides. As the concentra-
tion of CTP in the cell decreases then so does the inhibition of ATCase, and the resulting
increase in enzyme activity leads to the production of more pyrimidine nucleotides. is nega-
tive feedback inhibition is an important element of biochemical homeostasis within the cell.
However, in order to synthesize DNA and RNA, the cell requires not only pyrimidine nucleo-
tides but also purine nucleotides, and these are needed in roughly equal proportions. Purine
synthesis occurs through a dierent pathway, but interestingly the nal product, the purine
nucleotide adenosine triphosphate (ATP), is a potent activator of the enzyme ATCase. is is
logical, since when the cell contains high concentrations of purine nucleotides it will require
equally high concentrations of pyrimidine nucleotides in order for these two types of nucleotide
to combine to form the polymers DNA and RNA. us ATCase is able to regulate the produc-
tion of pyrimidine nucleotides within the cell according to cellular demand, and also to ensure
that pyrimidine nucleotide synthesis is synchronized with purine nucleotide synthesis—an ele-
gant biochemical mechanism for the regulation of an extremely important metabolic process.
ere are some rare, although important, cases of monomeric enzymes that have only one
substrate-binding site but are capable of demonstrating the sigmoidal reaction kinetics charac-
teristic of allosteric enzymes. Particularly noteworthy in this context is the monomeric enzyme
P.K. Robinson 21
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glucokinase (also called hexokinase IV), which catalyses the phosphorylation of glucose to glu-
cose-6-phosphate (which may then either be metabolized by the glycolytic pathway or be used
in glycogen synthesis). It has been postulated that this kinetic behaviour is a result of individual
glucokinase molecules existing in one of two forms—a low-anity form and a high-anity
form. e low-anity form of the enzyme reacts with its substrate (glucose), is then turned into
the high-anity form, and remains in that state for a short time before slowly returning to its
original low-anity form (demonstrating a so-called slow transition). erefore at high sub-
strate concentrations the enzyme is likely to react with a second substrate molecule soon aer
the rst one (i.e. while still in its high-anity form), whereas at lower substrate concentrations
the enzyme may transition back to its low-anity form before it reacts with subsequent sub-
strate molecules. is results in its characteristic sigmoidal reaction kinetics.
Origin, purification and uses of enzymes
Enzymes are ubiquitous
Enzymes are essential components of animals, plants and microorganisms, due to the fact that
they catalyse and co-ordinate the complex reactions of cellular metabolism.
Up until the 1970s, most of the commercial application of enzymes involved animal and
plant sources. At that time, bulk enzymes were generally only used within the food-processing
industry, and enzymes from animals and plants were preferred, as they were considered to be
free from the problems of toxicity and contamination that were associated with enzymes of
microbial origin. However, as demand grew and as fermentation technology developed, the
competitive cost of microbial enzymes was recognized and they became more widely used.
Compared with enzymes from plant and animal sources, microbial enzymes have eco-
nomic, technical and ethical advantages, which will now be outlined.
Economic advantages
e sheer quantity of enzyme that can be produced within a short time, and in a small produc-
tion facility, greatly favours the use of microorganisms. For example, during the production of
rennin (a milk-coagulating enzyme used in cheese manufacture) the traditional approach is to
use the enzyme extracted from the stomach of a calf (a young cow still feeding on its mother’s
milk). e average quantity of rennet extracted from a calf’s stomach is 10 kg, and it takes sev-
eral months of intensive farming to produce a calf. In comparison, a 1 000-litre fermenter of
recombinant Bacillus subtilis can produce 20 kg of enzyme within 12 h. us the microbial
product is clearly preferable economically, and is free from the ethical issues that surround the
use of animals. Indeed, most of the cheese now sold in supermarkets is made from milk coagu-
lated with microbial enzymes (so is suitable for vegetarians).
A further advantage of using microbial enzymes is their ease of extraction. Many of the
microbial enzymes used in biotechnological processes are secreted extracellularly, which
greatly simplies their extraction and purication. Microbial intracellular enzymes are also
oen easier to obtain than the equivalent animal or plant enzymes, as they generally require
fewer extraction and purication steps.
Animal and plant sources usually need to be transported to the extraction facility,
whereas when microorganisms are used the same facility can generally be employed for pro-
duction and extraction. In addition, commercially important animal and plant enzymes are
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oen located within only one organ or tissue, so the remaining material is essentially a waste
product, disposal of which is required.
Finally, enzymes from plant and animal sources show wide variation in yield, and may
only be available at certain times of year, whereas none of these problems are associated with
microbial enzymes.
Technical advantages
Microbial enzymes oen have properties that make them more suitable for commercial exploi-
tation. In comparison with enzymes from animal and plant sources, the stability of microbial
enzymes is usually high. For example, the high temperature stability of enzymes from thermo-
philic microorganisms is oen useful when the process must operate at high temperatures (e.g.
during starch processing).
Microorganisms are also very amenable to genetic modication to produce novel or
altered enzymes, using relatively simple methods such as plasmid insertion. The genetic
manipulation of animals and plants is technically much more dicult, is more expensive and
is still the subject of signicant ethical concern, especially in the U.K.
Enzymes may be intracellular or extracellular
Although many enzymes are retained within the cell, and may be located in specic subcellular
compartments, others are released into the surrounding environment. e majority of enzymes in
industrial use are extracellular proteins from either fungal sources (e.g. Aspergillus species) or bac-
terial sources (e.g. Bacillus species). Examples of these include α-amylase, cellulase, dextranase,
proteases and amyloglucosidase. Many other enzymes for non-industrial use are intracellular and
are produced in much smaller amounts by the cell. Examples of these include asparaginase, cata-
lase, cholesterol oxidase, glucose oxidase and glucose-6-phosphate dehydrogenase.
Enzyme purification
Within the cell, enzymes are generally found along with other proteins, nucleic acids, polysac-
charides and lipids. e activity of the enzyme in relation to the total protein present (i.e. the
specic activity) can be determined and used as a measure of enzyme purity. A variety of
methods can be used to remove contaminating material in order to purify the enzyme and
increase its specic activity. Enzymes that are used as diagnostic reagents and in clinical thera-
peutics are normally prepared to a high degree of purity, because great emphasis is placed on
the specicity of the reaction that is being catalysed. Clearly the higher the level of purica-
tion, the greater the cost of enzyme production. In the case of many bulk industrial enzymes
the degree of purication is less important, and such enzymes may oen be sold as very crude
preparations of culture broth containing the growth medium, organisms (whole or frag-
mented) and enzymes of interest. However, even when the cheapest bulk enzymes are utilized
(e.g. proteases for use in washing powders), the enzyme cost can contribute around 5–10% of
the nal product value.
At the end of a fermentation in which a microorganism rich in the required enzyme has been
cultured, the broth may be cooled rapidly to 5°C to prevent further microbial growth and sta-
bilize the enzyme product. e pH may also be adjusted to optimize enzyme stability. If the
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enzyme-producing organism is a fungus, this may be removed by centrifugation at low speed.
If the enzyme source is bacterial, the bacteria are oen occulated with aluminum sulfate or
calcium chloride, which negate the charge on the bacterial membranes, causing them to clump
and thus come out of suspension.
Extracellular enzymes are found in the liquid component of the pretreatment process.
However, intracellular enzymes require more extensive treatment. e biomass may be con-
centrated by centrifugation and washed to remove medium components. e cellular compo-
nent must then be ruptured to release the enzyme content. is can be done using one or more
of the following processes:
ball milling (using glass beads)
enzymic removal of the cell wall
freeze–thaw cycles
liquid shearing through a small orice at high pressure (e.g. within a French press)
osmotic shock
Separation of enzymes from the resulting solution may then involve a variety of separa-
tion processes, which are oen employed in a sequential fashion.
e rst step in an enzyme purication procedure commonly involves separation of the
proteins from the non-protein components by a process of salting out. Proteins remain in
aqueous solution because of interactions between the hydrophilic (water-loving) amino acids
and the surrounding water molecules (the solvent). If the ionic strength of the solvent is
increased by adding an agent such as ammonium sulfate, some of the water molecules will
interact with the salt ions, thereby decreasing the number of water molecules available to inter-
act with the protein. Under such conditions, when protein molecules cannot interact with the
solvent, they interact with each other, coagulating and coming out of solution in the form of a
precipitate. is precipitate (containing the enzyme of interest and other proteins) can then be
ltered or centrifuged, and separated from the supernatant.
Since dierent proteins vary in the extent to which they interact with water, it is possi-
ble to perform this process using a series of additions of ammonium sulfate, increasing the
ionic strength in a stepwise fashion and removing the precipitate at each stage. us such
fractional precipitation is not only capable of separating protein from non-protein compo-
nents, but can also enable separation of the enzyme of interest from some of the other pro-
tein components.
Subsequently a wide variety of techniques may be used for further purication, and steps
involving chromatography are standard practice.
Ion-exchange chromatography is oen eective during the early stages of the purica-
tion process. e protein solution is added to a column containing an insoluble polymer (e.g.
cellulose) that has been modied so that its ionic characteristics will determine the type of
mobile ion (i.e. cation or anion) it attracts. Proteins whose net charge is opposite to that of the
ion-exchange material will bind to it, whereas all other proteins will pass through the column.
A subsequent change in pH or the introduction of a salt solution will alter the electrostatic
forces, allowing the retained protein to be released into solution again.
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Gel ltration can be utilized in the later stages of a purication protocol to separate mol-
ecules on the basis of molecular size. Columns containing a bed of cross-linked gel particles
such as Sephadex are used. ese gel particles exclude large protein molecules while allowing
the entry of smaller molecules. Separation occurs because the larger protein molecules follow a
path down the column between the Sephadex particles (occupying a smaller fraction of the
column volume). Larger molecules therefore have a shorter elution time and are recovered rst
from the gel ltration column.
Affinity chromatography procedures can often enable purification protocols to be
substantially simplified. Typically, with respect to enzyme purification, a column would
be packed with a particulate stationary phase to which a ligand molecule such as a sub-
strate analogue, inhibitor or cofactor of the enzyme of interest would be firmly bound. As
the sample mixture is passed through the column, the enzyme interacts with, and binds,
to the immobilised ligand, being retained within the column as all of the other compo-
nents of the mixture pass through the column unrewarded. Subsequently a solution of the
ligand is introduced to the column to release (elute) and thereby recover the bound
enzyme from the column in a highly purified form.
Nowadays numerous alternative anity chromatography procedures exist that are able to
separate enzymes by binding to areas of the molecule away form their active site. Advances in
molecular biology enable us to purify recombinant proteins, including enzymes, through an-
ity tagging. In a typical approach the gene for the enzyme of interest would be modied to
code for a further short amino acid sequence at either the N- or C- terminal. For example, a
range of polyhistidine tagging procedures are available to yield protein products with six or
more consecutive histidine residues at their N- or C- terminal end. When a mixture contain-
ing the tagged protein of interest is subsequently passed through a column containing a nickel-
nitrilotriacetic acid (Ni-NTA) agarose resin, the histidine residues on the recombinant protein
bind to the nickel ions attached to the support resin, retaining the protein, whilst other protein
and non-protein components pass through the column. Elution of the bound protein can then
be accomplished by adding imidazole to the column, or by reducing the pH to 5-6 to displace
the His-tagged protein from the nickel ions.
Such techniques are therefore capable of rapidly and highly effectively isolating an
enzyme from a complex mixture in only one step, and typically provide protein purities of up
to 95%. If more highly puried enzyme products are required, other supplemental options are
also available, including various forms of preparative electrophoresis e.g. disc-gel electrophore-
sis and isoelectric focusing.
Finishing of enzymes
Enzymes are antigenic, and since problems occurred in the late 1960s when manufacturing
workers exhibited severe allergic responses aer breathing enzyme dusts, procedures have now
been implemented to reduce dust formation. ese involve supplying enzymes as liquids wher-
ever possible, or increasing the particle size of dry powders from 10 μm to 200–500 μm by
either prilling (mixing the enzyme with polyethylene glycol and preparing small spheres by
atomization) or marumerizing (mixing the enzyme with a binder and water, extruding long l-
aments, converting them into spheres in a marumerizer, drying them and covering them with
a waxy coat).
P.K. Robinson 25
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Industrial enzymology
Although many industrial processes, such as cheese manufacturing, have traditionally used
impure enzyme sources, oen from animals or plants, the development of much of modern
industrial enzymology has gone hand in hand with the commercial exploitation of microbial
enzymes. ese were introduced to the West in around 1890 when the Japanese scientist
Jokichi Takamine settled in the U.S.A. and set up an enzyme factory based on Japanese tech-
nology. The principal product was Takadiastase, a mixture of amylolytic and proteolytic
enzymes prepared by cultivating the fungus Aspergillus oryzae on rice or wheat bran.
Takadiastase was marketed successfully in the U.S.A. as a digestive aid for the treatment of dys-
pepsia, which was then believed to result from the incomplete digestion of starch.
Bacterial enzymes were developed in France by August Boidin and Jean Eront, who
in 1913 found that Bacillus subtilis produced a heat-stable α-amylase when grown in a liq-
uid medium made by extraction of malt or grain. e enzyme was primarily used within
the textile industry for the removal of the starch that protects the warp in the manufacture
of cotton.
In around 1930 it was found that fungal pectinases could be used in the preparation
of fruit products. In subsequent years, several other hydrolases were developed and sold
commercially (e.g. pectosanase, cellulase, lipase), but the technology was still fairly
Aer World War Two the fermentation industry underwent rapid development as meth-
ods for the production of antibiotics were developed. ese methods were soon adapted for
the production of enzymes. In the 1960s, glucoamylase was introduced as a means of hydro-
lysing starch, replacing acid hydrolysis. Subsequently, in the 1960s and 1970s, proteases were
incorporated into detergents and then glucose isomerase was introduced to produce sweeten-
ing agents in the form of high-fructose syrups. Since the 1990s, lipases have been incorpo-
rated into washing powders, and a variety of immobilized enzyme processes have been
developed (see section on enzyme immobilization), many of which utilize intracellular
Currently, enzymes are used in four distinct elds of commerce and technology (Table 6):
as industrial catalysts
as therapeutic agents
as analytic reagents
as manipulative tools (e.g. in genetics).
Of the thousands of dierent types of enzymes, about 95% are available from suppliers in
quantities ranging from μg to kg, provided essentially for research purposes. Around 40–50
enzymes are produced on an industrial scale (i.e. ranging from multiple kilograms to tonnes
per annum). e global enzyme market is currently dominated by the hydrolases, especially
the proteases, together with amylases, cellulases and lipases supplied either as liquid concen-
trates or as powders or granules that release the soluble enzyme on dissolution. Global produc-
tion is dominated by two companies, which between them supply more than two-thirds of the
global enzyme market, namely the Danish company Novozymes, with a market share of 47%,
and the U.S. company DuPont (which recently acquired Genencor), with 21%.
26 Essays in Biochemistry volume 59 2015
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Table 6. Uses of industrial enzymes.
Enzyme Reaction Source Application
Industrial catalysts
Acid proteases Protein digestion Aspergillus niger,
Kluyveromyces lactis
Milk coagulation in cheese manufacture
Alkaline proteases Protein digestion Bacillus species Detergents and washing powders
Aminoacylase Hydrolysis of acylated l–amino acids Aspergillus species Production of l–amino acids
α-Amylase Starch hydrolysis Bacillus species Conversion of starch to glucose or dextrans in the food industry
Amyloglucosidase Dextrin hydrolysis Aspergillus species Glucose production
β-Galactosidase Lactose hydrolysis Aspergillus species Hydrolysis of lactose in milk or whey
Glucose isomerase Conversion of glucose to fructose Streptomyces species High-fructose syrup production
Penicillin acylase Penicillin side-chain cleavage E. coli 6-APA formation for production of semi-synthetic penicillins
Therapeutic agents
l-Asparaginase Removal of l–asparagine essential for tumour
E. coli Cancer chemotherapy, particularly for leukaemia
Urokinase Plasminogen activation Human Removal of brin clots from bloodstream
Analytic reagents
Glucose oxidase Glucose oxidation Aspergillus niger Detection of glucose in blood
Luciferase Bioluminescence Marine bacteria or rey Bioluminescent assays involving ATP
Peroxidase Dye oxidation using H2O2Horseradish Quantication of hormones and antibodies
Urease Hydrolysis of urea to CO2 and NH3Jack bean Urea quantication in body uids
Manipulative tools
Lysozyme Hydrolysis of 1–4 glycosidic bonds Hen egg white Disruption of mucopeptide in bacterial cell walls
Nucleases Hydrolysis of phosphodiester bonds Various bacteria Restriction enzymes used in genetic manipulation to cut DNA
DNA polymerases DNA synthesis Thermus aquaticus DNA amplication used in the polymerase chain reaction
P.K. Robinson 27
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and distributed under the Creative Commons Attribution License 3.0.
e value of the world enzyme market has increased steadily from £110 million in 1960
to £200 million in 1970, £270 million in 1980, £1 000 million in 1990 and over £2 000 million
in 2010. Food and beverage enzymes represented the largest sector of the industrial enzymes
market in 2010, with a value of £750 million, and the market for enzymes for technical applica-
tions (including diagnostic applications, research and biotechnology) accounted for a further
£700 million. Estimates of future demand are in the range of £4 000–5 000 million between
2015 and 2016, growing at a rate of 6–7% annually. e developing economies of the Asia-
Pacic Region, the Middle East and Africa are now seen to be emerging as the fastest growing
markets for industrial enzymes.
Microbial enzymes are typically produced in batches by culturing the producing organ-
ism within a batch fermenter. Fermentation typically lasts between 30 and 150 h, with the opti-
mum enzyme yield for the process falling somewhere between the optimum biomass yield and
the point of maximal enzyme activity within the cells. Relatively small fermenters with a vol-
ume of 10–100 m3 are generally employed, allowing exibility where a number of dierent
products are being produced. Many production systems are optimized by means of a fed-batch
process, in which substrates are gradually fed into the reactor over the course of the fermenta-
tion, rather than being provided all at once at the start of the process. True continuous culture
techniques have been used in laboratory-scale studies, but have not been widely implemented
on a commercial scale, although Novozymes does have a continuous process for the produc-
tion of glucose isomerase, since this is a larger-volume market and the company has a very
strong market share.
Enzyme immobilization
During the production of commercially important products via enzymatic catalysis, soluble
enzymes have traditionally been used in batch processes that employ some form of stirred-
tank reactor (STR). In these processes, at the end of the batch run the product must be sepa-
rated from any unused substrate, and also from the enzyme catalyst. Removal of the enzyme at
this stage can be achieved by thermal denaturation (only if the product is thermostable) or by
ammonium sulfate precipitation or ultraltration. ese processes represent a costly down-
stream processing stage and generally render the enzyme inactive, so when a new batch run is
to be started a fresh batch of enzyme is required.
Immobilized enzyme systems, in contrast, ‘x’ the enzyme so that it can be reused many
times, which has a signicant impact on production costs. As a very simple example, if an
enzyme is mixed with a solution of warm (but not too hot) agar and this is allowed to set, the
enzyme will be entrapped (for the purposes of this example let us ignore the fact that the enzyme
will gradually leak out of this gel). e agar can then be cut up into cubes and these can be placed
in a STR, together with substrate, as shown in Figure 12. Again the reaction would be allowed to
proceed (and it might actually be slower due to diusional constraints and other eects described
later). At the end of the batch run the catalyst can now be easily separated from the product by
passing the reactor contents through a coarse mesh. Immediately an important downstream
processing step has been carried out and, just as importantly, the active enzyme has been
recovered so that it can be reused for the next batch run. is ease of separation of enzyme
from product is a major advantage of all immobilized systems over their counterparts that use
free (i.e. soluble) enzyme.
28 Essays in Biochemistry volume 59 2015
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is physical advantage of ease of reuse of immobilized biocatalysts is one of the main rea-
sons why such systems are favoured commercially. However, immobilization may also produce
biochemical changes that lead to enhanced biocatalyst stability, which may be manifested as:
an increased rate of catalysis
prolonged duration of catalysis
greater operational stability to extremes of pH, temperature, etc.
e particular advantage(s) conferred by immobilization will therefore dier from one
system to another. It should be noted that oen there may be no biochemical advantage at all,
and the simple physical advantage of ease of separation of the biocatalyst from the product
may be sucient to favour the commercial development of an immobilized process.
At this point one problem that will immediately spring to mind for most students is that
they have always been taught to fully mix all of the reagents of a reaction, yet the basic princi-
ple of immobilization is to partition the biocatalyst into a distinct phase, rather than mix it
homogeneously with the substrate. Will this not cause reaction rates to be low? e answer to
this question is yes, and the relationship between the activity of an immobilized system and a
non-immobilized system can be expressed as the eectiveness factor (η), where:
Effectiveness factor Activity of immobilized biocatalyst
=ttivity of non-immobilized biocatalyst
us an immobilized system with an eectiveness factor of 0.1 would show only 10% of
the activity of a non-immobilized system with the same amount of enzyme and operating
under the same conditions. At rst sight this might appear to be a major problem. However, if
it is possible to reuse the biocatalyst many times this is still economically viable, even with sys-
tems that have a low eectiveness factor. In principle, therefore, for economic viability:
Effectiveness factor Number of times of reuse 1×≥
us if an immobilized system has an eectiveness factor of 0.1 (i.e. 10%) and we can
reuse the biocatalyst 10 times, we essentially achieve the same overall catalytic activity with
Figure 12. Stirred-tank reactor containing immobilized enzyme.
P.K. Robinson 29
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and distributed under the Creative Commons Attribution License 3.0.
both the non-immobilized system and the immobilized one. However, if we are able to reuse
the biocatalyst 100 times we in fact obtain 10 times more total activity from the immobilized
system than from the equivalent non-immobilized system, so the immobilized system may be
economically preferable.
Once a biocatalyst has been immobilized it can also be put in a range of continuous-ow
reactors, enabling a continuous supply of substrate to be turned into product as it passes
through the reactor. e control of such continuous-ow reactors can be highly automated,
leading to considerable savings in production costs. For example, a STR can be easily modied
to produce a continuous-ow stirred-tank reactor (CSTR) (Figure 13a), in which the enzyme
is held within the reactor by a coarse mesh, and the product continuously ows out of the
reactor as substrate is pumped in. It is also possible to produce a packed-bed reactor (PBR)
(Figure 13b), in which the agar cubes are packed into a column and the substrate is pumped
through the bed without any need for stirring.
CSTRs and PBRs enable the enzyme to be reused many times before it needs to be
replaced. For example, in the production of high-fructose syrups, the immobilized glucose
isomerase enzyme would typically be used continuously for between 2 and 4 months, and only
aer this time (when its activity would have dropped to 25% of the original level) would it
need to be replaced.
e overall operating costs of continuous-ow reactors are oen signicantly lower than
those of equivalent batch processes. Batch reactors need to be emptied and relled frequently
at regular intervals. Not only is this procedure expensive, but it also means that there are
considerable periods of time when such reactors are not productive (so-called ‘downtime’).
Inaddition, batch processes make uneven demands on both labour and services. ey may
also result in pronounced batch-to-batch variations, as the reaction conditions change with
time, and they may be dicult to scale up, due to the changing power requirements for
Figure 13. Continuous-flow reactors. (a) Continuous-flow stirred-tank reactor
(CSTR). (b) Packed-bed reactor (PBR).
30 Essays in Biochemistry volume 59 2015
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ecient mixing. Due to their higher overall process eciency, continuous processes using
immobilized enzymes may be undertaken in production facilities that are around 10 to 100
times smaller than those required for equivalent batch processes using soluble enzymes.
erefore the capital costs involved in setting up the facility are also considerably lower.
Immobilization techniques
It should be noted that although the agar entrapment method described here has provided a use-
ful example, it is not a particularly eective form of immobilization. e high temperature
required to prevent the agar from setting may lead to thermal inactivation of the enzyme, and the
agar gel itself is very porous and will allow the enzyme to leak out into the surrounding solution.
ere are in fact thousands of dierent techniques of immobilization, all of which are
much more eective than our example. In general these techniques can be classied as belong-
ing to one of three categories (Figure 14):
covalent bonding
e physical adsorption of an enzyme to a supporting matrix is the oldest method of immobi-
lization. As early as 1916, J.M. Nelson and Edward G. Grin described the adsorption of yeast
invertase on to activated charcoal, and the subsequent use of this preparation for sucrose
hydrolysis. Over the years a variety of adsorbents have been used, including cellulose,
Sephadex, polystyrene, kaolinite, collagen, alumina, silica gel and glass. Such immobilization
procedures are extremely easy to perform, as the adsorbent and enzyme are simply stirred
together for a time (typically minutes to hours). e binding forces that immobilize the cata-
lyst on the support may involve hydrogen bonds, van der Waals forces, ionic interactions or
hydrophobic interactions. Such forces are generally weak in comparison with covalent
bonds—for example, a hydrogen bond has an energy content of about 20 kJ mol1, compared
with 200–500 kJ mol1 for a covalent bond. us, when using such methods, yields (i.e. the
amount of enzyme bound per unit of adsorbent) are generally low. In addition, adsorption is
generally easily reversed, and can lead to desorption of the enzyme at a critical time.
However, despite these limitations, such a method was used in the rst commercial immo-
bilized enzyme application, namely DEAE–Sephadex-immobilized -amino acid acylase, in
1969. DEAE–Sephadex is an ion-exchange resin that consists of an inert dextran particle
Figure 14. Immobilization techniques.
P.K. Robinson 31
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activated by the addition of numerous diethylaminoethyl groups. Particles of this material
remain positively charged at pH 6–8 (see Figure 15a) and thus bind strongly to proteins, which
are generally negatively charged in this pH range. If the pH is kept constant, the enzyme and sup-
port will remain ionically linked. However, when over time the enzyme loses its activity through
denaturation, the pH can be adjusted to a more acidic value, the old enzyme will be desorbed,
and the pH can then be readjusted back to pH 6–8 and a fresh batch of enzyme bound. us the
support matrix may be used many times, giving the process signicant economic benets.
Clearly DEAE–Sephadex immobilization is only of value for enzymes that have a neutral-
to-alkaline pH optimum. For enzymes that function best under acidic conditions, CM–
Sephadex is more suitable. is contains carboxymethyl groups that remain negatively charged
at pH 3.5–4.5 (Figure 15b). Proteins at this pH are generally positively charged and will thus
ionically bind to the support. Desorption of the enzyme will occur when the pH is adjusted to
a more alkaline value.
Due to the simplicity and controllability of this immobilization procedure, combined
with the economic benets of reuse of the support, ion-exchange materials are now widely
used as the method of choice in many industrial settings.
Covalent bonding
Immobilization of enzymes by covalent bonding to activated polymers is a widely used
approach since, although it is oen a tedious procedure, it is capable of producing an immobi-
lized enzyme that is rmly bound to its support. e range of polymers and chemical coupling
procedures that are used is enormous.
e history of covalent bonding for enzyme immobilization dates back to 1949, when F.
Michael and J. Ewers used the azide derivative of carboxymethylcellulose to immobilize a vari-
ety of proteins. Activated cellulose supports continue to be popular due to their inherent
advantages of high hydrophilicity, ready availability, potential for derivatization, and the ease
with which cellulose-based polymers can be produced either as particulate powders or as
membranous lms.
It is oen more eective not to build the reactive group into the cellulose itself, but
instead to use a chemical ‘bridge’ between the cellulose and the enzyme molecule. e require-
ments for such a bridging or linking molecule are that it must be small, and that once it has
reacted with the support it must have a further reactive group capable of reacting with the
enzyme. An example of such a bridging molecule is glutaraldehyde, which contains two alde-
hyde groups, one at either end of its (CH2)3 moiety. At neutral pH values the aldehyde groups
will react with free amino groups. Thus one end of the glutaraldehyde molecule may be
attached to the support, and the other to the enzyme.
Figure 15. Properties of (a) DEAE–Sephadex and (b) CM–Sephadex ion-exchange
32 Essays in Biochemistry volume 59 2015
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Covalently immobilized enzymes are strongly bound to their support, so when the pro-
teins denature they are dicult to remove (in contrast to adsorption, as described earlier).
erefore it is usual for both the enzyme and the support to be replaced. is may result in
higher operational costs compared with adsorption techniques in which the support may be
e entrapment of an enzyme can be achieved in a number of ways:
inclusion within the matrix of a highly cross-linked polymer
separation from the bulk phase by a semi-permeable ‘microcapsule’
dissolution in a distinct non-aqueous phase.
An important feature of entrapment techniques is that the enzyme is not in fact attached
to anything. Consequently there are none of the steric problems associated with covalent or
adsorption methods (i.e. the possibility of the enzyme binding in such a way that its active site
is obstructed by part of the supporting polymer matrix).
e example of an enzyme retained in agar, described earlier, is a useful illustration of
entrapment. A preferable alternative involves mixing the catalyst with sodium alginate gel
and extruding this into a solution of calcium chloride to produce solid calcium alginate parti-
cles. This technique has the advantage of not requiring the use of high temperatures.
However, although it is a popular activity in teaching laboratories, outside that setting it is
generally unsuitable for the immobilization of puried enzymes, as these are oen able to
leak out of the gel. Entrapment techniques for puried enzymes are more likely to involve
retaining the enzyme behind some form of ultraltration membrane. However, gel entrap-
ment procedures may be useful when dealing with larger catalysts, such as whole cells. For
example, gel-immobilized living yeast cells have been used successfully in the manufacture of
champagne by Moët & Chandon.
Immobilization: changes in enzyme properties
Earlier in this essay it was suggested that immobilization might change the properties of an
enzyme to enhance its stability. Initially it was believed that such enhanced stability resulted
from the formation of bonds between the enzyme and the supporting matrix that physically
stabilize the structure of the protein. Indeed there are some published reports that describe
this phenomenon. With regard to the stabilization of proteolytic enzymes, which oen exhibit
more prolonged activity in the immobilized state, this is most probably explained by the fact
that such proteases in free solution are prone to autodigestion (i.e. enzyme molecules cleave
the peptide bonds of adjacent enzyme molecules), a process that is largely prevented when
they are xed to a supporting matrix.
However, the eects of immobilization are more oen due to the supporting matrix chang-
ing the microenvironment around the enzyme and/or introducing diusional constraints that
modify the activity of the catalyst. Consider, for example, immobilization of the enzyme by
adsorption on to a polyanionic (negatively charged) support such as cellulose. If the substrate is
a cation (i.e. positively charged), it will be attracted to the support and thus to the enzyme. In
this case the enzyme might well display higher activity, as the substrate concentration in its
microenvironment would be higher than that in the surrounding bulk phase. Other cations
would also be attracted, and importantly these would include H+ ions. Thus the
P.K. Robinson 33
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microenvironment would also be enriched in H+ ions, so the pH surrounding the enzyme
would be lower than the pH of the bulk phase. Consequently the enzyme would also exhibit an
altered pH prole compared with that of its soluble counterpart.
In addition, the immobilization matrix might act as a barrier to the diusion of sub-
strates, products and other molecules. For example, if a high enzyme loading was put into a gel
particle and this was then immersed in substrate solution, the substrate would diuse into the
gel and rapidly be converted into product. Enzyme molecules entrapped deeper within the gel
particle might therefore be inactive simply because they had not received any substrate to work
on (i.e. all of the substrate was converted to product in the outer layers of the particle).
Although this is obviously somewhat inecient, it does have one useful eect. When over time
the enzyme within the system denatures, the loss of activity of the enzyme in the outer part of
the particle means that substrate will now diuse deeper into the particle to reach the previ-
ously unused core enzyme molecules. In eect this inner reserve of enzyme will oset the loss
of enzyme activity through denaturation, so the system will show little or no overall loss of
activity. is explains the observation that immobilized systems oen have a longer opera-
tional lifetime than their soluble equivalents.
In addition, it is of interest that enzymes bound to natural cell membranes (phospholipid
bilayers) within living cells will also probably demonstrate these eects, and immobilized sys-
tems thus provide useful models for the study of such membrane-bound proteins in living cells.
Immobilized enzymes at work
e major industrial processes that utilize immobilized enzymes are listed in Table 7. Sales of
immobilized enzymes peaked in 1990, when they accounted for about 20% of all industrial
enzyme sales, almost entirely due to the use of glucose isomerase for the production of sweet-
ening agents. Other commercial applications utilize penicillin acylase, fumarase, β–galactosi-
dase and amino acid acylase. Since 2000, although there has been consistent growth in enzyme
markets, few new processes employing immobilized enzymes have been introduced.
e following three examples highlight many of the biochemical, technological and eco-
nomic considerations relating to the use of immobilized enzymes on a commercial and indus-
trial scale.
Table 7. The major industrial processes that use immobilized enzymes.
Process Enzyme Production rate (ton year1)
High-fructose corn syrup production Glucose isomerase 107
Acrylamide production Nitrile hydratase 105
Transesterication of food oils Lipase 105
Lactose hydrolysis Lactase 105
Semi-synthetic penicillin production Penicillin acylase 104
l-aspartic acid production Aspartase 104
Aspartame production Thermolysin 104
34 Essays in Biochemistry volume 59 2015
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Production of high-fructose syrup
Undoubtedly the most signicant large-scale application of immobilized enzymes involves the
production of high-fructose corn syrup (HFCS). Although most of the general public believe
that sucrose is responsible for the ‘sweetness’ of food and drinks, there have been signicant
eorts to replace sucrose with alternative, and oen cheaper, soluble caloric sweetening agents.
HFCS is a soluble sweetener that has been used in many carbonated so drinks since the
1980s, including brand-name colas such as Coca-Cola and Pepsi-Cola. HFCS is produced by
the enzymatic digestion of starch derived from corn (maize). Developments in HFCS produc-
tion have been most prominent in countries such as the U.S.A., which have a high capacity to
produce starch in the form of corn, but which do not cultivate signicant amounts of sugar
cane or sugar beet, and must therefore import either the raw products (for processing) or the
rened sugar (sucrose) itself.
Simple corn syrups can be manufactured by breaking down starch derived from corn
using the enzyme glucoamylase alone or in combination with α-amylase. ese enzymes are
cheap and can be used in a soluble form. Since starch has to be extracted from corn at high tem-
peratures (because starch has poor solubility at low temperatures and forms very viscous solu-
tions), the process utilizes enzymes from thermophilic organisms, which have very high
temperature optima. Simple corn syrup is therefore composed predominantly of glucose, which
unfortunately has only 75% of the sweetness of sucrose. However, in order to make the syrup
sweeter the enzyme glucose isomerase, which catalyses the following reaction, can be employed:
Glucose isomerase
This enzyme (described previously in the section on properties and mechanisms of
enzyme action) will produce a roughly 50:50 mixture of glucose and fructose at equilibrium,
and since fructose has 150% of the sweetness of sucrose, this glucose:fructose mixture will
have a similar level of sweetness to sucrose. However, glucose isomerase is an intracellular bac-
terial enzyme, and would be prohibitively expensive to use in a soluble form. is makes it an
ideal candidate for use in an immobilized process.
The first glucose isomerase enzyme to be isolated was obtained from species of
Pseudomonas in 1957, and more useful enzymes were isolated throughout the 1960s from spe-
cies of Bacillus and Streptomyces. In 1967, the Clinton Corn Processing Company of Iowa,
U.S.A. (later renamed CPC International) introduced a batch process that utilized an immobi-
lized glucose isomerase enzyme, and by 1972 the company had developed a continuous pro-
cess for the manufacture of HFCS containing 42% fructose using a glucose isomerase enzyme
immobilized on a DEAE ion-exchange support.
During the late 1970s, advances in enzymology, process engineering and fractionation
technology led to the production of syrups with a higher fructose content, and today HFCS
containing 55% fructose is generally produced, and is commonly used in so drinks, although
42% fructose syrups are still also produced for use in some processes, including the production
of bakery foodstus.
In 2010, the U.S. production of HFCS was approximately 8 million metric tons, account-
ing for 37% of the U.S. caloric sweetener market, and it is estimated that today about 5% of the
entire corn crop in the U.S.A. is used to produce HFCS.
P.K. Robinson 35
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and distributed under the Creative Commons Attribution License 3.0.
Hydrolysis of lactose
Within the dairy industry the production of 1 kg of cheese requires about 10 litres of milk, and
produces about 9 litres of whey as a waste product. Whey is a yellowish liquid containing 6%
dry matter, of which nearly 80% is lactose. e enzyme lactase (β-galactosidase) may be used
to break down lactose to its constituent monosaccharides, namely glucose and galactose,
which are more soluble than lactose, and have potential uses as carbon sources in microbial
fermentation, and can also be used as caloric sweeteners.
LactoseGlucose Galactose
Valio Ltd of Finland has developed arguably the most successful commercial process
for the treatment of whey. Using a lactase enzyme obtained from Aspergillus, immobilized by
adsorption and cross-linked on to a support resin, whey syrups are produced that have been
utilized as an ingredient in drinks, ice cream and confectionery products. e Aspergillus
enzyme has an acid pH optimum of 3–5, and by operating at low pH the process avoids
excessive microbial contamination. Treatment plants that utilize 600-litre columns have
been built in Finland, and these are used to treat 80 000 litres of whey per day. is technol-
ogy has also been used to produce whey syrups in England (by Dairy Crest) and in Norway.
Similar technology can also be used to remove lactose from milk. Lactose-free milk is
produced for consumption by those who have lactose intolerance (a genetic condition), and
also for consumption by pets such as cats, which are oen unable to digest lactose easily. e
rst industrial processing facility to use immobilized lactase to treat milk was opened in 1975,
when Centrale del Latte of Milan, Italy, utilized a batch process in which yeast (Saccharomyces)
lactase, with a neutral pH optimum of 6–8, was immobilized within hollow permeable bres.
is process was capable of treating 10 000 litres of milk per day, and was operated at low tem-
perature to prevent microbial contamination.
Production of semi-synthetic penicillins
High yields of natural penicillins are obtained from species of the fungus Penicillium through
fermentation processes. However, over the years many microbial pathogens have become
resistant to natural penicillins, and are now only treatable with semi-synthetic derivatives.
ese are produced through cleavage of natural penicillin, such that the G or V side chain is
removed from the 6-aminopenicillanic acid (6-APA) nucleus of the molecule:
Penicillin G or V G or
Penicillin acylase
VV side chain 6-APA+
ereaer, by attachment of a chemically dierent side chain, a semi-synthetic penicillin
product (e.g. ampicillin, amoxicillin) can be formed. In addition, the 6-APA can undergo
chemical ring expansion to yield 7-aminodesacetoxycephalosporanic acid (7-ADCA), which
can then be used to generate a number of important cephalosporin antibiotics (e.g. cephalexin,
cephradine, cefadroxil).
e development of immobilized penicillin G acylase dates back to research conducted in
1969 by University College London and Beecham Pharmaceuticals in the U.K. Penicillin G
acylases are intracellular enzymes found in E. coli and a variety of other bacteria, and the
36 Essays in Biochemistry volume 59 2015
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Beecham process immobilized the E. coli enzyme on a DEAE ion-exchange support. Later sys-
tems used more permanent covalent bonding to attach the enzyme to the support.
In the 1980s and 1990s, world production of penicillins was dominated by European man-
ufacturers, which accounted for production of around 30 000 tonnes of penicillin per annum,
75% of which was used for the manufacture of semi-synthetic penicillins and cephalosporins.
However, over the past 10 years, due to increasing costs of labour, energy and raw materials,
more bulk manufacturing has moved to the Far East, where China, Korea and India have
become major producers. e market currently suers from signicant overcapacity, which has
driven down the unit cost of penicillin and cephalosporin products. However, penicillins and
cephalosporins still represent one of the world’s major biotechnology markets, with annual sales
of about £10 000 million, accounting for 65% of the entire global antibiotics market.
Enzymes in analysis
Enzymes have a wide variety of uses in analytical procedures. eir specicity and potency
allow both detection and amplication of a target analyte. ‘Wet chemistry’ enzyme-based
assays for the detection and quantication of a variety of substances, including drugs, are
widespread. Enzymes also play a key role in immunodiagnostics, oen being used as the agent
to amplify the signal—for example, in enzyme-linked immunosorbent assays (ELISAs). Within
DNA-ngerprinting technology, the enzyme DNA polymerase plays a key role in the ampli-
cation of DNA molecules in the polymerase chain reaction. However, ‘wet chemistry’ analyti-
cal methods are increasingly being replaced by the use of biosensors—that is, self-contained
integrated devices which incorporate a biological recognition component (usually an immobi-
lized enzyme) and an electrochemical detector (known as a transducer).
Much of the technological development of biosensors has been motivated by the need to meas-
ure blood glucose levels. In 2000, the World Health Organization estimated that over 170 mil-
lion people had diabetes, and predicted that this gure will rise to over 360 million by 2030. In
view of this, many companies have made signicant investments in R&D programmes that
have led to the availability of a wide variety of glucose biosensor devices.
In 1962, Leland Clark Jr coined the term ‘enzyme electrode’ to describe a device in which
a traditional electrode could be modied to respond to other materials by the inclusion of a
nearby enzyme layer. Clark’s ideas became a commercial reality in 1975 with the successful
launch of the Yellow Springs Instruments (YSI) model 23A glucose analyser. is device incor-
porated glucose oxidase together with a peroxide-sensitive electrode to measure the hydrogen
peroxide (H2O2) produced during the following reaction:
GlucoseO Gluconic acidHO
+→ +22
In this device, the rate of H2O2 formation is a measure of the rate of the reaction, which
depends on the concentration of glucose in solution, thus allowing the latter to be estimated.
As was discussed earlier, in enzyme-catalysed reactions the relationship between substrate
concentration and reaction rate is not linear, but hyperbolic (as described by the Michaelis–
Menten equation). is is also true for the glucose oxidase within a biosensor. However, we
P.K. Robinson 37
© 2015 Authors. This is an open access article published by Portland Press Limited
and distributed under the Creative Commons Attribution License 3.0.
may engineer a more linear relationship by ensuring that the enzyme is either behind or within
a membrane through which the glucose must diuse before it reacts with the enzyme. is
means that the system becomes diusionally, rather than kinetically, limited, and the response
is then more linearly related to the concentration of glucose in solution.
Over the years the YSI model 23A glucose analyser has been replaced by a range of much
more advanced models. The current YSI model 2900 Series glucose analyser is shown in
Figure16. is instrument has a 96-sample rack that enables batches of samples to be run, with
the analysis of each sample taking less than a minute. e instrument can measure the glucose
content of whole blood, plasma or serum, and requires only 10 μl of sample per analysis. e
membrane-bound glucose oxidase typically only needs to be replaced every 3 weeks, thereby
reducing the cost of analysis. ese systems also oer advanced data-handling and data-storage
In addition, these instruments can be modied to analyse a wide variety of other sub-
stances of biological interest, simply by incorporating other oxidase enzymes into the mem-
brane (Table 8).
To enable diabetic patients to take their own blood glucose measurements, small hand-
held biosensors have also been developed, which are in fact technologically more advanced
because the enzyme and transducer are more intimately linked on the sensor surface. e
rst device of this type was launched in 1986 by Medisense, and was based on technology
developed in the U.K. at Craneld and Oxford Universities. e ExacTech blood glucose
meter was the size and shape of a pen, and used disposable electrode strips. is device was
followed by a credit card-style meter in 1989. Such devices again rely on glucose oxidase as
the biological component, but do not measure the reaction rate via the production (and
Figure 16. A laboratory-scale glucose analyser.
Photograph supplied courtesy of YSI (UK) Limited.
38 Essays in Biochemistry volume 59 2015
© 2015 Authors. This is an open access article published by Portland Press Limited
and distributed under the Creative Commons Attribution License 3.0.
detection) of H2O2. Instead they rely on direct measurement of the rate of electron ow from
glucose to the electrode surface. e reactions that occur within this device may be summa-
rized as follows:
GlucoseGO-FADGluconic acid GO -FADH
GO -FADHFerrocene
+→ +
mediator GO -FAD Ferrocene mediator
Xoxidized reduced
and at the electrode surface:
Ferrocene mediatorFerrocene mediator
reducedoxidized e→+
where GOx-FAD represents the FAD redox centre of glucose oxidase in its oxidized form, and
GOx-FADH2 represents the reduced form.
Basically electrons are removed from the glucose molecules and passed via the enzyme to
the ferrocene mediator, which then donates them to the working electrode surface, resulting in
the generation of an electrical current that is directly proportional to the rate of oxidation of
glucose, and thus proportional to the glucose concentration in the sample.
Medisense, whose only product was its blood glucose meter, was bought by Abbott
Diagnostics in 1996, and Abbott-branded devices continued to use and develop this technol-
ogy for some time.
In 1999, Therasense marketed a glucose meter that represented the next generation of
sensing technology, and integrated the enzyme even more closely with the electrode.
Originally developed by Adam Heller at the University of Texas in the 1990s, wired-
enzyme electrodes do not rely on a soluble mediator such as the ferrocene used in the
Medisense devices. Instead the enzyme is immobilized in an osmium-based polyvinyl imi-
dazole hydrogel in which the electrons are passed from enzyme to electrode by a series of
fixed electroactive osmium centres that shuttle the electrons onward in a process called
‘electron hopping.’
In 2004, Abbott Diagnostics purchased erasense, and instruments such as the FreeStyle
Freedom Lite meter range produced by Abbott Diabetes Care (Figure 17) now incorporate this
wired-enzyme technology. Devices of this type are highly amenable to miniaturization.
Continuous measuring devices are becoming increasingly available, and may well revolu-
tionize the control of certain disease conditions. For example, with regard to diabetes, devices
Table 8. Composition of enzyme membranes available for analysers with a
peroxide-sensitive electrode as the transducer.
Analyte Enzyme Reaction
Glucose Glucose oxidase β-D-glucose + O2 gluconic acid + H2O2
Alcohol Alcohol oxidase Ethanol + O2 acetaldehyde + H2O2
Lactic acid Lactate oxidase l-lactate + O2 pyruvate + H2O2
Lactose Galactose oxidase Lactose + O2 galactose dialdehyde derivative + H2O2
P.K. Robinson 39
© 2015 Authors. This is an open access article published by Portland Press Limited
and distributed under the Creative Commons Attribution License 3.0.
such as the FreeStyle Navigator range from Abbott Diabetes Care use the same wired-enzyme
technology as that described earlier, but now incorporate this into a tiny lament about the
diameter of a thin hypodermic needle. is is inserted approximately 5 mm under the skin to
measure the glucose level in the interstitial uid that ows between the cells. e unit is
designed to remain in situ for up to 5 days, during which time it can measure the glucose con-
centration every minute. A wireless transmitter sends the glucose readings to a separate
receiver anywhere within a 30-metre range, and this can then issue an early warning alarm to
alert the user to a falling or rising glucose level in time for them to take appropriate action and
avoid a hypoglycaemic or hyperglycaemic episode.
In addition, experimental units have already been developed that link continuous glucose
biosensor measurement systems with pumps capable of gradually dispensing insulin such that
the diabetic condition is automatically and reliably controlled, thereby avoiding the traditional
peaks and troughs in glucose levels that occur with conventional glucose measurement and the
intermittent administration of insulin.
erefore, looking to the future, we may condently expect to see the development of
biosensor systems that can continuously monitor a range of physiologically important analytes
and automatically dispense the required medication to alleviate the symptoms of a number of
long-term chronic human illnesses.
Figure 17. A hand-held glucose biosensor suitable for personal use.
Photograph supplied courtesy of Abbott Diabetes Care.
40 Essays in Biochemistry volume 59 2015
© 2015 Authors. This is an open access article published by Portland Press Limited
and distributed under the Creative Commons Attribution License 3.0.
Closing remarks
For the sake of conciseness, this guide has been limited to some of the basic principles of enzy-
mology, together with an overview of the biotechnological applications of enzymes. It is
important to understand the relationship between proteins and the nucleic acids (DNA and
RNA) that provide the blueprint for the assembly of proteins within the cell. Genetic engineer-
ing is thus predominantly concerned with modifying the proteins that a cell contains, and
genetic defects (in medicine) generally relate to the abnormalities that occur in the proteins
within cells. Much of the molecular age of biochemistry is therefore very much focused on the
study of the cell, its enzymes and other proteins, and their functions.
Recommended reading and key
1. Historically important landmark papers
(inchronological order)
Takamine, J. (1894) Process of making diastatic enzyme. U.S. Pat. 525,823. Describes the rst
commercial exploitation of semi-puried enzymes in the West.
Briggs, G.E. and Haldane, J.B.S. (1925) A note on the kinetics of enzyme action. Biochem. J. 19,
338–339. A classic paper in which the steady-state assumption was introduced into the
derivation of the Michaelis–Menten equation.
Koshland, Jr, D.E. (1958) Application of a theory of enzyme specificity to protein synthesis. Proc.
Natl Acad. Sci. U.S.A. 44, 98–104. Describes the proposal of an ‘induced t’ mechanism of
substrate binding.
Clark, Jr, L.C. and Lyons, C. (1962) Electrode systems for continuous monitoring in cardiovascular
surgery. Ann. N.Y. Acad. Sci. 102, 29–45. Introduces the concept of a biosensor for
measuring blood glucose levels during surgery.
Monod, J., Wyman, H. and Changeux, J.P. (1965) On the nature of allosteric transitions: a plausible
model. J. Mol. Biol. 12, 88–118. Describes the ‘concerted’ model of transitions of allosteric
proteins in which all constituent monomers are in either the T-state or the R-state.
Koshland, Jr, D.E., Némethy, G. and Filmer, D. (1966) Comparison of experimental binding data
and theoretical models in proteins containing subunits. Biochemistry 5, 365–385. Describes
the ‘sequential’ model of transitions of allosteric proteins in which protein moves through
hybrid structures with some monomers in the T-state and some in the R-state.
Updike, S.J. and Hicks, G.P. (1967) The enzyme electrode. Nature 214, 986–988. Describes the
simplication of the electrochemical assay of glucose by immobilizing and thereby stabilizing
the glucose oxidase enzyme.
Tramontano, A., Janda, K.D. and Lerner, R.A. (1986) Catalytic antibodies. Science 234, 1566–
1570. Pollack, S.J., Jacobs, J.W. and Schultz, P.G. (1986) Selective chemical catalysis by an
7-ADCA, 7-aminodesacetoxycephalosporanic acid; 6-APA, 6-aminopenicillanic acid;
ATCase, aspartate transcarbamoylase; CSTR, continuous-ow stirred-tank reactor; CTP,
cytidine triphosphate; DFP, diisopropyl uorophosphate; EC, Enzyme Commission; ELISA,
enzyme-linked immunosorbent assay; GUT, glucose-1-phosphate uridylyltransferase;
HFCS, high-fructose corn syrup; PBR, packed-bed reactor; PFK, phosphofructokinase;
STR, stirred-tank reactor.
P.K. Robinson 41
© 2015 Authors. This is an open access article published by Portland Press Limited
and distributed under the Creative Commons Attribution License 3.0.
antibody. Science 234, 1570–1573. The rst reports of antibody proteins that demonstrate
catalytic activity.
Johnson, K.A. and Goody, R.S. (2011) The original Michaelis constant: translation of the 1913
Michaelis–Menten paper. Biochemistry 50, 8264–8269. A modern translation, commentary
and re-analysis of the original 1913 paper, Die Kinetik der Invertinwirkung.
Taylor, A.I., Pinheiro, V.B., Smola, M.J., Morgunov, A.S., Peak-Chew, S., Cozens, C., Weeks, K.M.,
Herdewijn, P. and Holliger, P. (2015) Catalysts from synthetic genetic polymers. Nature 518,
427–430. Describes the rst articial enzymes to be created using synthetic biology.
2. Enzyme principles
Changeux, J.-P. (2013) 50 years of allosteric interactions: the twists and turns of the models. Nat.
Rev. Mol. Cell Biol. 14, 819–829.
Kamata, K., Mitsuya, M., Nishimura, T., Eiki, J. and Nagata, Y. (2004) Structural basis for allosteric
regulation of the monomeric allosteric enzyme human glucokinase. Structure 12, 429–438.
3. Enzyme applications
Adrio, J.L. and Demain, A.L. (2014) Microbial enzymes: tools for biotechnological processes.
Biomolecules 4, 117–139.
Clarke, S.F. and Foster, J.R. (2012) A history of blood glucose meters and their role in self-
monitoring of diabetes mellitus. Br. J. Biomed. Sci. 69, 83–93.
Fernandes, P. (2010) Enzymes in food processing: a condensed overview on strategies for better
biocatalysts. Enzyme Res. 2010, 862537.
Vashist, S.K., Zheng, D., Al-Rubeaan, K., Luong, J.H.T. and Sheu, F.-S. (2011) Technology behind
commercial devices for blood glucose monitoring in diabetes management: a review. Anal.
Chim. Acta 703, 124–136.
Vellard, M. (2003) The enzyme as drug: application of enzymes as pharmaceuticals. Curr. Opin.
Biotechnol. 14, 444–450.
Woodley, J.M. (2008) New opportunities for biocatalysis: making pharmaceutical processes
greener. Trends Biotechnol. 26, 321–327.
4. Useful textbooks
Bisswanger, H. (2008) Enzyme Kinetics: Principles and Methods, 2nd edn, Wiley-VCH, Weinheim,
Germany. Available online and as hard copy. A user-friendly and comprehensive treatise on
enzyme kinetics.
Buchholz, K., Kasche, V. and Bornscheuer, U.T. (2012) Biocatalysts and Enzyme Technology,
2nd edn, Wiley-VCH, Weinheim, Germany. Best-selling textbook that provides an instructive
and comprehensive overview of our current knowledge of biocatalysis and enzyme
Copeland, R.A. (2013) Evaluation of Enzyme Inhibitors in Drug Discovery: A Guide for Medicinal
Chemists and Pharmacologists, 2nd edn, John Wiley & Sons, Inc., Hoboken, NJ. Provides
thorough coverage of both the principles and applications of enzyme inhibitors.
McGrath, M.J. and Scanaill, C.N. (2014) Sensor Technologies: Healthcare, Wellness and
Environmental Applications, Apress Media, LLC, New York. Available online. Covers sensor
technologies and their clinical applications, together with broader applications that are
relevant to wellness, tness, lifestyle and the environment.
Trevan, M.D. (1980) Immobilized Enzymes: An Introduction and Applications in Biotechnology, John
Wiley & Sons, Chichester. An older text, and difcult to nd except in libraries, but it provides
an introductory text for non-experts, and as yet there is no other book that fulls this role.
Whitehurst, R.J. and van Oort, M. (2009) Enzymes in Food Technology, 2nd edn, Wiley-Blackwell,
Chichester. Provides comprehensive coverage of the widespread use of enzymes in food-
processing improvement and innovation.
... Environmental factors such as pH and temperature can influence the rate of enzymecatalyzed reactions through reversible or irreversible modifications in the enzyme structure [21]. Therefore, the definition of optimum pH and temperature profile provides ...
... Environmental factors such as pH and temperature can influence the rate of enzymecatalyzed reactions through reversible or irreversible modifications in the enzyme structure [21]. Therefore, the definition of optimum pH and temperature profile provides valuable information for the utilization of enzymes in bioprocesses. ...
... Environmental factors such as pH and temperature can influence t catalyzed reactions through reversible or irreversible modification structure [21]. Therefore, the definition of optimum pH and temperatu valuable information for the utilization of enzymes in biopro determination of fermentative conditions, the FFase was characterized temperature and it was observed that enzymes present maximum acti of 5-7 and 60 °C, as observed in Figure 3. Dapper et al. [22] report an o for A. versicolor FFase, on the other side, Choukade and Kango [6] r FTase activity at pH 7.0 for mycelial Aspergillus tamarii enzyme temperature influence, the optimum FTase activity was observed at 6 the activity was lower, presenting 17.47% relative activity. ...
Full-text available
β-fructofuranosidases (FFases) are enzymes involved in sucrose hydrolysis and can be used in the production of invert sugar and fructo-oligosaccharides (FOS). This last is an important prebiotic extensively used in the food industry. In the present study, the FFase production by Aspergillus tamarii Kita UCP 1279 was assessed by solid-state fermentation using a mixture of wheat and soy brans as substrate. The FFase presents optimum pH and temperature at 5.0–7.0 and 60 °C, respectively. According to the kinetic/thermodynamic study, the FFase was relatively stable at 50 °C, a temperature frequently used in industrial FOS synthesis, using sucrose as substrate, evidenced by the parameters half-life (115.52 min) and D-value (383.76 min) and confirmed by thermodynamic parameters evaluated. The influence of static magnetic field with a 1450 G magnetic flux density presented a positive impact on FFase kinetic parameters evidenced by an increase of affinity of enzyme by substrate after exposition, observed by a decrease of 149.70 to 81.73 mM on Km. The results obtained indicate that FFases present suitable characteristics for further use in food industry applications. Moreover, the positive influence of a magnetic field is an indicator for further developments of bioprocesses with the presence of a magnetic field.
... Therefore, a mechanistic pathway of enzyme promiscuity has significant importance in the study of enzyme evolutions 5 . Usually, the enzymes show promiscuity in the substrate selectivity, but they retain the nature of native reaction 6,7 . Mechanistic studies of enzyme promiscuity show that some strategic mutations change the substrate recognition pattern, which, in turn, causes promiscuity in enzymes 8- 10 . ...
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L-Homoserine Kinase is crucial in the biosynthesis of Threonine, Isoleucine, and Methionine. Using computational tools herein, we provide new insight into the catalytic mechanism of L-homoserine kinase, showing a direct involvement of H139 as a catalytic base, in contrast to the previous consensus, where no involvement of a catalytic base was proposed. The proposed mechanism agrees with the finding that an H138L mutation reduces the Kinase activity but enhances a promiscuous function as ATPase activity
... Misalnya, mereka memiliki peran penting dalam produksi zat pemanis dan modifikasi antibiotik, mereka digunakan dalam bubuk pencuci dan berbagai produk pembersih, dan mereka memainkan peran kunci dalam perangkat analitik dan pengujian yang memiliki efek klinis, forensik dan lingkungan. Kata 'enzim' pertama kali digunakan oleh ahli fisiologi Jerman Wilhelm Kühne pada tahun 1878, ketika ia menjelaskan kemampuan ragi untuk menghasilkan alkohol dari gula, dan berasal dari kata Yunani en (berarti 'di dalam') dan zume (artinya 'ragi') (Robinson, 2015). ...
... High enzyme activities recorded in well watered sorghum bicolor may be ascribed to the presence of adequate amount of water [33][34][35][36]. Rate of hydrolysis is usually high in cells with high water contents because the water may serve as substrate for enzyme activation [37,36]. According to Huang and Song [38], in mature seeds, spores or pollens, with comparatively low hydrolysis level, enzyme activities are always extremely feeble. ...
Enzymes play significant roles in metabolic processes of seeds. Therefore, this study evaluated osmoregulatory potential of some osmoprotectants on activities of some hydrolytic enzymes in the seeds of two cultivars (SOSAT.C-88 and CV. LCIC 9702) of sorghum bicolor. Matured seeds of the two cultivars were harvested and prepared for alpha, beta, total amylase and proteinase activities assay. The osmoprotectants produced significant variations on the enzymes at 10 and 14 days (DA) of 8 weeks after treatments (WAT). Seeds of well-watered SOSAT.C-88 produced higher alpha (2.10 IU/ml), beta (1.70 IU/ml) and total amylase activities (3.30 IU/ml) at 14 days (DA). Higher alpha (2.01 IU/ml and total amylase activities (2.61 IU/ml) were recorded in the seeds of CV. LCIC 9702 well-watered at 14 days DA 8WAT. Furthermore, total amylase activities (3.87 IU/ml) were recorded in the seeds produced by CV. LCIC 9702 well-watered at 14 days DA. Significant increase was noticed in beta (1.14 IU/ml) and alpha amylase (1.58 IU/ml) in the seeds of CV. LCIC 9702 treated with mycorrhiza. CV. LCIC 9702 well watered produced highest proteinase activities (1.57 U/ml) while least of the parameters were recorded in SOSAT.C-88 and CV. LCIC 9702 droughted. In conclusion, the osmoprotectants had regulatory effects on the activities of hydrolytic enzymes therefore the use of the osmoprotectants in farming should be encouraged.
... However, González et al. [71] found that the anthocyanin composition of the blackcurrant extracts obtained from pectinase enzyme and ultrasound-assisted did not significantly differ. The extraction time, temperature and the state of raw material might influence the effect of enzymes on the substrate [72]. Despite the higher content of petunidin-3-O-rutinoside(trans-p-coumaroyl)-5-O-glucoside content in pectinase-assisted extraction (Fig. 1), the TAC of the extracts obtained from different extraction methods did not differ ( Table 2). ...
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Lycium ruthenicum, commonly known as black goji berry, is a rich anthocyanin source containing a high amount of monoacylated anthocyanins. This study investigates the effect of different extraction methods to extract anthocyanins from black goji berry for food application. Different hot water extraction conditions were applied to investigate the effect of specific substrate: solvent ratio (1:15 and 1:20 (w/v)), extraction time (30 and 60 min) and extraction temperature (40, 50 and 60 °C) on the extraction yield, total anthocyanin content (TAC) and the total phenolic content (TPC) of the anthocyanin extracts. Best hot water extraction conditions for obtaining an anthocyanin extract with high TAC (13.8 ± 1.14 mg CGE/g), TPC (69.7 ± 2.50 mg of GAE/g), and extraction yield (48.3 ± 3.25%) consuming less solvent, time and heat were substrate: solvent ratio of 1: 15 (w/v), extraction temperature of 50 °C, and extraction time of 30 min. The effect of pectinase, ultrasound, and microwave on hot water extraction of anthocyanins from black goji berry was investigated using the best conditions for hot water extraction. Pectinase-assisted extraction [1.5% (w/v) pectinase, substrate: solvent ratio of 1:15 (w/v) at 50 °C for 30 min] was the best extraction method to extract black goji berry anthocyanins demonstrating higher extraction yield, TAC, TPC, and the highest percentage of petunidin-3-O-(trans-p-coumaroyl)-rutinoside-5-O-glucoside.
... Enzymes are biocatalyst proteins (except ribozymes which are nucleic acids rather than proteins and behave like enzymes) that speed up the biological process that occurs inside living organisms [1]. Enzymes are generally composed of one or more chains of an amino acid called polypeptide chains. ...
Enzymes are highly specific and highly sensitive biocatalyst proteins that play important roles in various life processes. As they are proteins, thus, they are composed of amino acids joined together to form chains. These amino acids are linked by peptide bonds that form between the amino-terminal and carboxylic end. There is the multifaceted application of enzymes in various sectors that include food, textile, paints, pharmaceuticals, leather, oil industries, etc. There is a wide range of sources available for the extraction of enzymes. The commercially important enzymes are generally harvested from microbial sources. Some enzymes are produced extracellularly while some enzymes are produced intracellularly. The production of this bioactive compound could be enhanced by applying suitable optimization techniques, genetic engineering tools, and other modern techniques. One of the major challenges in the commercial production of enzymes is their extraction in pure form without losing their properties. Extraction of enzymes starts from upstream processing that mainly includes two types of fermentation; one is submerged fermentation and another one is solid-state fermentation. After upstream processing, downstream processing is followed which includes cell disruption, filtration, sedimentation and centrifugation, flocculation and coagulation, and chromatography. Then, enzyme purification strategies are followed (salting-out method, dialysis, gel filtration, ion-exchange chromatography, gel electrophoresis. The purpose of down streaming is to purify and concentrate the enzyme from the complex bulk matrix. A significant amount of total production cost is contributed by downstream processing. The review discusses the industrial importance of enzymes and their downstream processing techniques economically and sustainably.
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Thermostable enzymes are enzymes that can withstand elevated temperatures as high as 50 °C without altering their structure or distinctive features. The potential of thermostable enzymes to increase the conversion rate at high temperature has been identified as a key factor in enhancing the efficiency of industrial operations. Performing procedures at higher temperatures with thermostable enzymes minimises the risk of microbial contamination, which is one of the most significant benefits. In addition, it helps reduce substrate viscosity, improve transfer speeds, and increase solubility during reaction operations. Thermostable enzymes offer enormous industrial potential as biocatalysts, especially cellulase and xylanase, which have garnered considerable amount of interest for biodegradation and biofuel applications. As the usage of enzymes becomes more common, a range of performance-enhancing applications are being explored. This article offers a bibliometric evaluation of thermostable enzymes. Scopus databases were searched for scientific articles. The findings indicated that thermostable enzymes are widely employed in biodegradation as well as in biofuel and biomass production. Japan, the United States, China, and India, as along with the institutions affiliated with these nations, stand out as the academically most productive in the field of thermostable enzymes. This study's analysis exposed a vast number of published papers that demonstrate the industrial potential of thermostable enzymes. These results highlight the significance of thermostable enzyme research for a variety of applications.
With 39,400 km2 of coastal and marine areas artificialized and an increasing demand due to the growing global population—9 billion by 2050—it has become necessary to find ways to mitigate futures constructions impacts on biodiversity. This study explores how civil engineering can take further technical measures to enhance marine biodiversity, in a real and valuable “win-win” strategy. The global aim is to integrate eco-engineering practices within coastal projects and include ecological targets (e.g., the diversity and speed of biological colonization) early, at the project design stage, with the same level efforts for technical, social, and economic studies. Concrete is the most useful material for coastal infrastructure construction. Therefore, enhance its positive impact on colonization that is by far one of the key points for developers and coastal managers. To this end, the latest research regarding the bioreceptivity of concrete is reviewed, focusing on the characteristics of the marine environment that affect the colonization of concrete and the organisms involved. From this base of publications, the intrinsic and environmental parameters that can influence the intrinsic and the extrinsic bioreceptivity of concrete have been updated, specifically operating the link with the mechanisms leading to the colonization of concrete and biofilm formation, which hasn't been done before. Based on the persistence of their significant effect (after 78 days of immersion in seawater), the intrinsic parameters that support greater biocolonization are classified from more to less effective in the following order: surface roughness (190%) > chemical composition (slag cement instead Portland cement) (136%) > chemical composition (presence of formwork oil) (106%). Lastly, both the ecological effect and the positive and negative effects of biofilm formation on the durability of concrete were analysed to provide clear and operational results for future concrete coastal construction implementation for decision makers.
Lantibiotics are a group of synthesized polypeptides containing unusual amino acids such as 3-methyllanthionine and lanthionine. Lantibiotics are Bacteriocins, which disrupt membrane integrity and are produced by gram-positive bacteria. In addition, these lantibiotics provide an alternative dual mechanism inhibition of cell growth (cell wall inhibition and membrane pore formation) when they have low resistance. Recently, the synthesis of these Bacteriocins has attracted much attention due to the combination of genome biology and mining, which has led to high activity and specificity to other species. Although high throughput bioprocess screening and strain optimization have been studied previously, it affects the production of lantibiotics due to complex impurities. However, once the optimization and scaling for the mass production stages are done, it will be much easier and not time-consuming. In this chapter, we discuss (1) the structure and functional properties that influence lantibiotics production, (2) the chemical synthesis and the economic feasibility of using lantipeptides, (3) in vitro bioengineering synthesis, and (4) combined bioprocess strategies to increase the amount of yield of Lantibiotics (5) the viability of the bioproduction process of lantibiotics. We further discuss the current applications and propose a measure to enhance the production of lantibiotics on a large scale.
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The emergence of catalysis in early genetic polymers such as RNA is considered a key transition in the origin of life1, pre-dating the appearance of protein enzymes. DNA also demonstrates the capacity to fold into three-dimensional structures and form catalysts in vitro. However, to what degree these natural biopolymers comprise functionally privileged chemical scaffolds for folding or the evolution of catalysis is not known. The ability of synthetic genetic polymers (XNAs) with alternative backbone chemistries not found in nature to fold into defined structures and bind ligands raises the possibility that these too might be capable of forming catalysts (XNAzymes). Here we report the discovery of such XNAzymes, elaborated in four different chemistries (arabino nucleic acids, ANA; 2'-fluoroarabino nucleic acids, FANA; hexitol nucleic acids, HNA; and cyclohexene nucleic acids, CeNA) directly from random XNA oligomer pools, exhibiting in trans RNA endonuclease and ligase activities. We also describe an XNA–XNA ligase metalloenzyme in the FANA framework, establishing catalysis in an entirely synthetic system and enabling the synthesis of FANA oligomers and an active RNA endonuclease FANAzyme from its constituent parts. These results extend catalysis beyond biopolymers and establish technologies for the discovery of catalysts in a wide range of polymer scaffolds not found in nature. Evolution of catalysis independent of any natural polymer has implications for the definition of chemical boundary conditions for the emergence of life on Earth and elsewhere in the Universe.
Full-text available
Microbial enzymes are of great importance in the development of industrial bioprocesses. Current applications are focused on many different markets including pulp and paper, leather, detergents and textiles, pharmaceuticals, chemical, food and beverages, biofuels, animal feed and personal care, among others. Today there is a need for new, improved or/and more versatile enzymes in order to develop more novel, sustainable and economically competitive production processes. Microbial diversity and modern molecular techniques, such as metagenomics and genomics, are being used to discover new microbial enzymes whose catalytic properties can be improved/modified by different strategies based on rational, semi-rational and random directed evolution. Most industrial enzymes are recombinant forms produced in bacteria and fungi.
Full-text available
The concept of indirect or 'allosteric' interaction between topographically distinct sites, and the subsequent 1965 Monod-Wyman-Changeux (MWC) model for the conformational change mediating them, arose around 50 years ago. Many classic regulatory proteins (including haemoglobin, Asp transcarbamylase and nicotinic acetylcholine receptor) follow the central paradigm of the MWC model, which has been expanded and challenged as a result of novel technologies. Importantly, the concept of allosteric interaction has aided our understanding of human diseases and drug design.
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Food and feed is possibly the area where processing anchored in biological agents has the deepest roots. Despite this, process improvement or design and implementation of novel approaches has been consistently performed, and more so in recent years, where significant advances in enzyme engineering and biocatalyst design have fastened the pace of such developments. This paper aims to provide an updated and succinct overview on the applications of enzymes in the food sector, and of progresses made, namely, within the scope of tapping for more efficient biocatalysts, through screening, structural modification, and immobilization of enzymes. Targeted improvements aim at enzymes with enhanced thermal and operational stability, improved specific activity, modification of pH-activity profiles, and increased product specificity, among others. This has been mostly achieved through protein engineering and enzyme immobilization, along with improvements in screening. The latter has been considerably improved due to the implementation of high-throughput techniques, and due to developments in protein expression and microbial cell culture. Expanding screening to relatively unexplored environments (marine, temperature extreme environments) has also contributed to the identification and development of more efficient biocatalysts. Technological aspects are considered, but economic aspects are also briefly addressed.
The second edition of this successful book highlights the widespread use of enzymes in food processing improvement and innovation, explaining how they bring advantages. The properties of different enzymes are linked to the physical and biochemical events that they influence in food materials and products, while these in turn are related to the key organoleptic, sensory and shelf life qualities of foods. Fully updated to reflect advances made in the field over recent years, new chapters in the second edition look at the use of enzymes in the reduction of acrylamide, in fish processing and in non-bread cereal applications such as flour confectionery. Genetic modification of source organisms (GMO) has been used to improve yields of purer enzymes for some time now but the newer technology of protein engineering (PE) of enzymes has the potential to produce purer, more targeted products without unwanted side activities, and a chapter is also included on this important new topic. Authors have been selected not only for their practical working knowledge of enzymes but also for their infectious enthusiasm for the subject. The book is aimed at food scientists and technologists, ingredients suppliers, geneticists, analytical chemists and quality assurance personnel.
Self-monitoring blood glucose (SMBG) systems have the potential to play an important role in the management of diabetes and in the reduction of risk of serious secondary clinical complications. This review describes the transition from simple urine sugar screening tests to sophisticated meter and reagent strip systems to monitor blood glucose. Significant developments in design and technology over the past four decades are described since the first meter was introduced in 1970. Factors that have influenced this evolution and the challenges to improve analytical performance are discussed. Current issues in the role of SMBG from the clinical, patient and manufacturer perspectives, notably adherence, costs and regulations, are also considered.
The blood glucose monitoring devices (BGMDs) are an integral part of diabetes management now-a-days. They have evolved tremendously within the last four decades in terms of miniaturization, rapid response, greater specificity, simplicity, minute sample requirement, painless sample uptake, sophisticated software and data management. This article aims to review the developments in the technologies behind commercial BGMD, especially those in the areas of chemistries, mediators and other components. The technology concerns, on-going developments and future trends in blood glucose monitoring (BGM) are also discussed.
Nearly 100 years ago Michaelis and Menten published their now classic paper [Michaelis, L., and Menten, M. L. (1913) Die Kinetik der Invertinwirkung. Biochem. Z. 49, 333-369] in which they showed that the rate of an enzyme-catalyzed reaction is proportional to the concentration of the enzyme-substrate complex predicted by the Michaelis-Menten equation. Because the original text was written in German yet is often quoted by English-speaking authors, we undertook a complete translation of the 1913 publication, which we provide as Supporting Information . Here we introduce the translation, describe the historical context of the work, and show a new analysis of the original data. In doing so, we uncovered several surprises that reveal an interesting glimpse into the early history of enzymology. In particular, our reanalysis of Michaelis and Menten's data using modern computational methods revealed an unanticipated rigor and precision in the original publication and uncovered a sophisticated, comprehensive analysis that has been overlooked in the century since their work was published. Michaelis and Menten not only analyzed initial velocity measurements but also fit their full time course data to the integrated form of the rate equations, including product inhibition, and derived a single global constant to represent all of their data. That constant was not the Michaelis constant, but rather V(max)/K(m), the specificity constant times the enzyme concentration (k(cat)/K(m) × E(0)).
The immunoglobulin MOPC167, which binds the transition state analog p-nitrophenylphosphorylcholine with high affinity, catalyzed the hydrolysis of the corresponding carbonate 1. MOPC167 catalysis displayed saturation kinetics with catalytic constant (kcat) = 0.4 min-1 and Michaelis constant (Km) = 208 microM, showed substrate specificity, and was inhibited by p-nitrophenylphosphorylcholine. The rate of the reaction was first order in hydroxide ion concentration between pH 6.0 and 8.0. The lower limit for the rate of acceleration of hydrolysis by the antibody above the uncatalyzed reaction was 770. This study begins to define the rules for the generation of catalytic antibodies.