Bogumil Zelent

Bogumil Zelent
University of Pennsylvania | UP · Biophysical Instrumentation Laboratory, Department of Biochemistry and Biophysics

Ph.D.

About

92
Publications
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Publications

Publications (92)
Article
Full-text available
Five variants of glucokinase (ATP-D-hexose-6-phosphotransferase, EC 2.7.1.1) including wild type and single Trp mutants with the Trp residue at positions 65, 99, 167 and 257 were prepared. The fluorescence of Trp in all locations studied showed intensity changes when glucose bound, indicating that conformational change occurs globally over the enti...
Article
Full-text available
Foods contain a plethora of aromatic molecules—natural colors, synthetic dyes, flavors, vitamins, antioxidants, etc.—that are luminescent, exhibiting prompt fluorescence or delayed phosphorescence. Although food autofluorescence has been used to detect specific contaminants (e.g., aflatoxins) or to authenticate specific foods (olive oil), much of t...
Article
Allura red (AR) fluorophore, a common dye in the food industry, displays a broad emission spectrum in water (visible-to-near infrared region of the electromagnetic spectrum) and has a remarkably short fluorescence lifetime of about 10 ps. This short lifetime does not depend on the emission (observation) wavelength. We examined time responses of AR...
Conference Paper
The photophysical properties of generally-recognized-as-safe (GRAS) food dyes, such as Allura Red (AR), Tartrazine (TR), Sunset Yellow (SY) and Fast Green (FG), have rarely been reported. All these dyes exhibit very weak emission in common fluid solvents, which can explain the limited information on their photophysical properties. A significant enh...
Article
Hepatic glucose phosphorylation by glucokinase (GK) is regulated by glucokinase regulatory protein (GKRP). GKRP forms a cytosolic complex with GK followed by nuclear import and storage, leading to inhibition of GK activity. This process is initiated by low glucose but reversed nutritionally by high glucose and fructose or pharmacologically by GK ac...
Article
Full-text available
Hepatic glucose phosphorylation by glucokinase (GK) is regulated by glucokinase regulatory protein (GKRP). GKRP forms a cytosolic complex with GK followed by nuclear import and storage, leading to inhibition of GK activity. This process is initiated by low glucose but reversed nutritionally by high glucose and fructose or pharmacologically by GK ac...
Article
Full-text available
Glucokinase activators (GKAs) are being developed and clinically tested for potential antidiabetic therapy. The potential benefits and limitations of this approach continue to be intensively debated. To contribute to the understanding of experimental pharmacology and therapeutics of GKAs, we have tested the efficacy of one of these agents (Piraglia...
Article
We investigated how glycerol, urea, glucose and a GKA influence kinetics and stability of wild-type and mutant GK. Glycerol and glucose stabilized GK additively. Glycerol barely affected the TF spectra of all GKs but decreased k(cat), glucose S(0.5) and K(D) values and ATP K(M) while leaving cooperativity unchanged. Glycerol sensitized all GKs to G...
Article
Full-text available
GK (glucokinase) is activated by glucose binding to its substrate site, is inhibited by GKRP (GK regulatory protein) and stimulated by GKAs (GK activator drugs). To explore further the mechanisms of these processes we studied pure recombinant human GK (normal enzyme and a selection of 31 mutants) using steady-state kinetics of the enzyme and TF (tr...
Article
Full-text available
We performed genome-wide mutagenesis in C57BL/6J mice using N-ethyl-N-nitrosourea to identify mutations causing high blood glucose early in life and to produce new animal models of diabetes. Of a total of 13 new lines confirmed by heritability testing, we identified two semi-dominant pedigrees with novel missense mutations (Gck(K140E) and Gck(P417R...
Article
Full-text available
GK (glucokinase) is activated by glucose binding to its substrate site, is inhibited by GKRP (GK regulatory protein) and stimulated by GKAs (GK activator drugs). To explore further the mechanisms of these processes we studied pure recombinant human GK (normal enzyme and a selection of 31 mutants) using steady-state kinetics of the enzyme and TF (tr...
Article
Glucokinase (GK ; EC 2.7.1.1.) phosphorylates and regulates glucose metabolism in insulin-producing pancreatic beta-cells, hepatocytes, and certain cells of the endocrine and nervous systems allowing it to play a central role in glucose homeostasis . Most importantly, it serves as glucose sensor in pancreatic beta-cells mediating glucose-stimulated...
Article
Full-text available
The photochemical reaction products of carbazole with carbon tetrachloride in ethanol have been isolated and identified along with photoproducts in the irradiated solution of carbazole in pure CCl4 using water and ethanol added after the irradiation. This allowed us to discuss the complex mechanism of secondary photochemical changes in the carbazol...
Article
In part I of this series of papers we proposed the mechanism of electron transfer as the primary photochemical reaction in the carbazole – carbon tetrachloride system along with a secondary photochemical reaction initiated by transformations of the radical cation of carbazole in the solvent cage resulting in intermediates:In this paper we discuss t...
Article
Full-text available
The mechanism of the photodecomposition of N-ethylcarbazole (NEC) in the presence of carbon tetrachloride has been discussed on the basis of the photoproducts identified. The photodissociation of the N-ethyl bond and the electron transfer in the transiently formed ex-CT complex, , have been proposed as the primary photochemical processes involved i...
Article
The synthesis, electronic spectroscopy, and photoactivity of two polysebacate oligomers with pendant donor–acceptor bichromophores of the alkylcarbazole–dinitrofluorene type (P1) and the alkylcarbazole–trinitrofluorenone carboxylic acid ester type (P2) are reported. The crystal structure of the basic acceptor chromophore A2 and donor-acceptor bichr...
Article
Full-text available
The stability of bovine lactoperoxidase to denaturation by guanidinium-HCl, urea, or high temperature was examined by differential scanning calorimetry (DSC) and tryptophan fluorescence. The calorimetric scans were observed to be dependent on the heating scan rate, indicating that lactoperoxidase stability at temperatures near Tm is controlled by k...
Article
We report the use of infrared (IR) spectroscopy to detect ice crystals in biological solutions. The method is based on the temperature dependence of the OH bending and stretch bands of water. By using mixtures of D(2)O and H(2)O, water's absorption bands can be made to be on-scale in transmission mode. Water's stretch band moves to lower frequency...
Article
The influence of proteins and solutes on hysteresis of freezing and melting of water was measured by infrared (IR) spectroscopy. Of the solutes examined, poly-L-arginine and flounder antifreeze protein produced the largest freezing point depression of water, with little effect on the melting temperature. Poly-L-lysine, poly-L-glutamate, cytochrome...
Article
Full-text available
Tryptophan fluorescence was used to study GK (glucokinase), an enzyme that plays a prominent role in glucose homoeostasis which, when inactivated or activated by mutations, causes diabetes mellitus or hypoglycaemia in humans. GK has three tryptophan residues, and binding of D-glucose increases their fluorescence. To assess the contribution of indiv...
Article
The role of water's H-bond percolation network in acid-assisted proton transfer was studied in water and glycerol solutions and in sugar glasses. Proton transfer rates were determined by the fluorescence of pyrene-1-carboxylate, a compound with a higher pK in its excited state relative to the ground state. Excitation of pyrene-1-COO- produces fluor...
Article
Full-text available
Pyrene-1-carboxy acid has a pK of 4 in the ground state, and a pK of 8 in the excited state. Fluorescence spectra of the acid and base forms are presented as a function of solvent and temperature. Ab initio quantum calculations indicate that the bond between the ring system and the carboxyl group has aromatic character that becomes stronger upon ex...
Article
The heme in horseradish peroxidase (HRP) was replaced by phosphorescent Pt-mesoporphyrin IX (PtMP), which acted as a phosphorescent marker of oxygen quenching and allowed comparison with another probe, Pd-mesoporphyrin IX (Khajehpour et al. (2003) Proteins 53, 656-666). Benzohydroxamic acid (BHA), a competitive inhibitor of the enzyme, was also use...
Article
Fluorescence imaging of cells and tissue can be used to evaluate beta-NADH redox and location. At low temperature, beta-NADH fluorescence intensity increases and therefore sensitivity of imaging increases. In this paper, the temperature dependence of fluorescence was evaluated for beta-NADH in glycerol/water solution and in trehalose/sucrose glass....
Article
Pyrene-1-carboxylic acid has a pK of 4.0 in the ground state and 8.1 in the singlet electronic excited state. In the pH range of physiological interest (pH approximately 5-8), the ground state compound is largely ionized as pyrene-1-carboxylate, but protonation of the excited state molecule occurs when a proton donor reacts with the carboxylate dur...
Article
The iron of lactoperoxidase is predominantly high-spin at ambient temperature. Optical spectra of lactoperoxidase indicate that the iron changes from high-spin to low-spin in the temperature range from room temperature to 20 K. The transformation is independent of whether the enzyme is in glycerol/water or solid sugar glass. Addition of the inhibit...
Article
Water is a highly polar molecule that is capable of making four H-bonding linkages. Stability and specificity of folding of water-soluble protein macromolecules are determined by the interplay between water and functional groups of the protein. Yet, under some conditions, water can be replaced with sugar or other polar protic molecules with retenti...
Article
In order to correlate how the solvent affects emission properties of tryptophan, the fluorescence and phosphorescence emission spectra of tryptophan and indole model compounds were compared for solid sugar glass (trehalose/sucrose) matrix and glycerol/water solution and under the same conditions, these matrices were examined by infrared spectroscop...
Article
Fluorescent analogues of the potent and highly selective delta-opioid antagonist TIPP (H-Tyr-Tic-Phe-Phe-OH) and TIP (H-Tyr-Tic-Phe-OH) containing the exceptionally environmentally sensitive fluorescent amino acid beta-(6'-dimethylamino-2'-naphthoyl)alanine (Aladan [Ald]) in place of Phe3 were synthesized. The Ald3- and D-Ald3 analogues of TIPP and...
Article
Full-text available
Infrared absorption spectra for liquid and ice H 2O and D 2O and for protonated and deuterated glycerol/water glasses are compared in the spectral range of 1000-4000 cm -1 and the temperature range of 295-12 K. As temperature decreases, the absorbance bands of the OH and OD stretching modes of glycerol/water solution shift to lower frequency and th...
Article
The heme of horseradish peroxidase is buried in the protein, but a channel from the protein surface connects the aqueous solution to the heme site. Ferric horseradish peroxidase has an absorption band at 640 nm that is attributed to a charge-transfer (CT) transition between the a 2u HOMO of π electrons of the porphyrin ring and the d xy /d yz orbit...
Article
Full-text available
Dansylated analogues of the potent and selective micro opioid peptide agonist [Dmt(1)]DALDA (H-Dmt-D-Arg-Phe-Lys-NH(2); Dmt = 2',6'-dimethyltyrosine) were prepared either by substitution of N(beta)-dansyl-alpha,beta-diaminopropionic acid or N(epsilon)-dansyllysine for Lys(4), or by attachment of a dansyl group to the C-terminal carboxamide function...
Article
Full-text available
Polarized steady-state fluorescence and fluorescence excitation spectra as well as time-resolved fluorescence for B-phycoerythrin (B-PE) from red algae, Porphyridium cruentum, embedded in polyvinyl stretched films were measured. The lifetimes of polarized fluorescence were analyzed using exponential components and fractal models. The interactions b...
Article
H-Dmt-D-Arg-Phe-Lys-NH2 (Dmt=2',6'-dimethyltyrosine) ([Dmt1] DALDA) is a highly potent and selective micro opioid peptide agonist capable of producing an antinociceptive effect after systemic administration. Fluorescent analogues of [Dmt1] DALDA containing either beta-dansyl-L-alpha,beta-diaminopropionic acid [Dap(dns)] or beta-anthraniloyl-L-alpha...
Article
Stoichiometric exchange of GTP for GDP on heterotrimeric G protein α (Gα) subunits is essential to most hormone and neurotransmitter initiated signal transduction. Gαs are stably activated in a Mg2+ complex with GTPTγS, a nonhydrolyzable GTP analogue that is reported to bind Gα with very high affinity. Yet, it is common to find that substantial amo...
Article
Polarized absorption and fluorescence spectra of bacteriochlorophyll c and green photosynthetic bacterium Prostheecochloris aestuarii cells and cell fragments embedded in stretched polymer film were measured. In pigment samples the artificial oligomers of bacteriochlorophyll c (with absorption about 750 nm) and other forms of this pigment and bacte...
Article
Short distance interactions of chlorophyll a with violaxanthin (Viol) were studied in monolayers at the air-water interface and in Langmuir-Blodgett films. The surface pressure–area (π–A) isotherms for Chl a, Viol, and Chl a–Viol mixtures clearly indicate the formation of two types of complexes between Chl a and Viol with the stoichiometric ratios...
Article
The phenomenological distance-dependent quenching (DDQ) model was employed to investigate the character of the interaction between volatile anesthetics (VAs) and the plasma membrane Ca2+-ATPase (PMCA). The simultaneous analysis of the frequency-domain and steady-state data of tryptophan (Trp) fluorescence quenching by a VA points to a specific char...
Article
We examined the time-resolved and steady-state fluorescence quenching of N-acetyl-l-tryptophanamide (NATA) by acrylamide and iodide, over a range of viscosities in propylene glycol. The quenching of NATA by acrylamide and iodide results in heterogeneity of the intensity decay which increases with the quencher concentration. We attribute the complex...
Article
The decays of the polarized components of fluorescence (excited at 410 nm by a 70 fs laser flash) of whole bacteria Prosthecochloris aestuarii cells, their fragments and isolated bacteriochlorophyll c molecules located in isotropic and stretched polymer films have been measured and analysed using exponential components which in the literature data...
Article
Alpha transducin Uyptophan fluorescence was used to assay conversion from the GDP to CTP bound stale. Despite a lOpM Kd of GTP for transducin, l-'microM GTP K 1/2 was required for fluorescence increase. Later addition of more GTP could not improve initially weak fluorescence of lower GTP, suggest ing an irréversible process with i n ar.ti vat abili...
Article
Trp fluorescence of the two Up protein, alpha transducin, increases threefold upon replacement of GDP by GTP. Crystal structures show the environment and configuration of W127 remains unchanged while that of W207 in the GTP'ase domain is altered materially. Thus, the three-fold net increase in activated trp intensity might reflect a much larger cha...
Chapter
The green sulfur bacterium Prosthecochloris aestuarii contains light-harvesting structure called chlorosomes [1,2]. The main pigment of chlorosomes is bacteriochlorophyll (BChl) c, with a small admixture of BChl a. The proteins contribute little to the structure of the rods contained in chlorosome envelope [3,4]. BChl c occurs in chlorosomes mostly...
Article
Full-text available
Fluorescence quenching of Nile Blue by amines is thought to be due to electron transfer to the excited dye molecule from the amine electron donor. We used electron transfer quenching of Nile blue byN,N-diethylaniline in propylene glycol as a model system for an interaction which depends exponentially on distance. We investigated the time dependence...
Article
Full-text available
Fluorescence quenching of Nile Blue by amines is thought to be due to electron transfer to the excited dye molecule from the amine electron donor. We used electron transfer quenching of Nile blue byN,N-diethylaniline in propylene glycol as a model system for an interaction which depends exponentially on distance. We investigated the time dependence...
Article
We report results of frequency-domain and steady-state measurements of the fluorescence quenching of p-bis[2-(5-phenyloxazolyl)]benzene (POPOP) when quenched by bromoform (CHBr3), methyl iodide (CH3I), potassium iodide (KI), 1,2,4-trimethoxybenzene (TMB), or N,N-diethylaniline (DEA). The quenching efficiency of these compounds decreased in the orde...
Article
The chlorophyll a (Chl a) and its mixture with β-carotene were embedded in nematic liquid crystal - anisotropic matrix. The decays of fluorescence were measured at two wavelengths: 680nm and 715nm and analyzed using biexponential and fractal models. Fractal model fits better to decay of fluorescence emitted at 680nm by samples with Chl a alone. For...
Article
Chlorophyll b (Chl b) in model systems occures in several forms. The relationship between these forms and the forms occurring in organisms is not yet clear. Chl b aggregation has been investigated less than that of Chl a. In this paper, several spectral features, e.g. fluorescence lifetimes in the picosecond time range, time-resolved delayed lumine...
Article
The decay of fluorescence of green bacteria cells immobilized in polymer film was measured and analyzed using two models, taking into account (1) that every emitter is in the presence of energy acceptors, and (2) that the fluorescence decay is the superposition of monoexponential decays of various emitters. The first model fitted better to the emis...
Article
The photoelectrochemical behavior of chlorophyll a and pheophytin a monolayers, deposited on tin oxide (SnO2) optically transparent electrodes (OTE) by means of the Langmuir-Blodgett technique, has been investigated. The photocurrent action spectra coincide with the absorption spectra of photosynthetic pigment monolayers at the SnO2/solution interf...
Article
Fluorescence lifetime in the ps range, polarized absorption, polarized fluorescence spectra and delayed luminescence time resolved spectra were measured for chlorophyll a solutions with and without beta-carotene addition in nematic liquid crystal. Photoacoustic spectra of the same samples at various frequencies of light modulation were also taken....
Article
The chlorophyll (chl) a-cytochrome (cyt) c mixed system was studied in Langmuir films at the air-water interface and Langmuir-Blodgett films. Surface pressure-molecular area isotherms measured for pure and mixed components were discussed in terms of ideal mixing processes. The negative deviations from ideality observed at cyt c molar fractions lowe...
Article
Abstract We used GHz frequency-domain fluorometry to investigate the time-dependent intensity decays of N-acetyl -L-trytophanamide (NATA) when collisionally quenched by acrylamide in propylene glycol at 20°C. The intensity decays of NATA became increasingly heterogeneous in the presence of acrylamide. The NATA intensity decays were not consistent w...
Article
Chlorophyll a (Chl) in most model systems (monolayers, fluid solvents, adsorbed layers, and polymer films) occurs in three forms: `dry monomers' (isolated from interaction with water), hydrated dimers and oligomers built from such dimers; but in nematic liquid crystal (LC) cell `dry monomers' are predominant. It is a competition between the various...
Article
Full-text available
Frequency-domain fluorometry was used to investigate the time- dependent intensity decays of N-acetyl-L-tryptophanamide (NATA) when collisionally quenched by acrylamide and iodide in propylene glycol at 20 degree(s)C. The intensity decays of NATA became increasingly heterogeneous in the presence of quenching, and the steady-state Stern-Volmer plots...
Article
The fluorescence lifetimes in the picosecond time range of various aggregated forms of chlorophyll a (Chl a) in different media (wet n-haxane, adsorbed layers and polymer films) were measured. Photographs of Chl a and Chl b poly(vinyl alcohol) (PVA) samples containing pigment oligomers are compared and discussed on the basis of previous and present...
Article
The photoelectrochemical, absorption and fluorescence properties of pheophytin a mono- and multilayers, deposited on optically transparent tin oxide electrodes and quartz slides were investigated. Spectra of photocurrents coincided with the absorption spectra of photosynthetic pigment in monolayers at the SnO[sub 2]/solution interfaces. The anodic...
Article
Chlorophyll a (Chl) in most model systems (monolayers, fluid solvents, adsorbed layers, and polymer films) occurs in three forms: `dry monomers' (isolated from interaction with water), hydrated dimers and oligomers built from such dimers; but in nematic liquid crystal (LC) cell `dry monomers' are predominant. It is a competition between the various...
Article
Phycobilisomes oriented in stretched polymer films exhibit anisotropy of absorption and fluorescence. Up to now it was not clear in which way, by the deformation of their shape or by orientation of undeformed phycobilisome disk, this anisotropy of chromophore absorption and emission is reached. The photographs of two different kind of phycobilisome...
Article
Full-text available
We examined the time-dependent intensity decays of N-acetyl-L-tryptophanamide (NATA) when collisionally quenched by acrylamide in propylene glycol over a range of temperatures. The intensity decays of NATA became increasingly heterogeneous in the presence of acrylamide. The NATA intensity decays were not consistent with the Collins-Kimball radiatio...
Article
The interfacial tension measurements of dry and wet chlorophyll a at an octane—water interface show differences in adsorption behavior of the pigment depending on its aggregation state. Optical properties were also investigated using absorption and Fourier transform-infrared spectroscopy, along with fluorescence (excitation and emission) measuremen...
Article
Polarized absorption and fluorescence spectra as well as lifetime of fluorescence (τ) of the mixtures of chlorophyll a (Chl a) and chlorophyll b (Chl b) in anisotropic polyvinyl alcohol (PVA) films were measured. Two mixtures with various concentrations ratios of Chl a to Chl b were investigated. For comparison, the fluorescence excitation and emis...
Article
Polarized absorption and fluorescence spectra as well as lifetime of fluorescence (tau) of the mixtures of chlorophyll a (Chl a) and chlorophyll b (Chl b) in anisotropic polyvinyl alcohol (PVA) films were measured. Two mixtures with various concentrations ratios of Chl a to Chl b were investigated. For comparison, the fluorescence excitation and em...
Article
Anacystis nidulans cyanobacteria and their fragments embedded in unstretched, uniaxial and skew (two axes of stretching forming an angle of 40 degrees) stretched poly(vinyl alcohol) films have been investigated. Polarized absorption spectra for uniaxial and skew stretching samples were measured. Both unoriented and oriented samples were photographe...