[Show abstract][Hide abstract] ABSTRACT: Prickly pear LOX activity was detected in the membrane fractions of the fruit extracts at various stages of ripening. LOX specific activity was very low in the fruit of wild plants at the green stage (0.49 0.04) and increased with fruit ripening, more than doubling in the ripened fruit (1.22 0.06). Moreover, it was not influenced by the cultivar, whereas it was considerably increased (13.3 1.4) by agronomic processes to which prickly pear plants are submitted to improve the organoleptic properties of fruits. The apparent molecular mass of the enzyme was estimated to be 96 kDa. The enzyme had an optimum pH value of 5.5 and a clear specificity for linolenic acid, which was oxidized at a rate one and a half times that of linoleic acid, under the same reaction conditions. The involvement of prickly pear LOX in the flavor biosynthesis of the fruit is supposed.
[Show abstract][Hide abstract] ABSTRACT: The biological activities of a series of mono- and oligosaccharides (beta-xylosides and alpha-glucosides) of 9-fluorenylmethanol were investigated together with mono-beta-galactoside and beta-glucoside of this aglycone, produced by biocatalytic routes. By using marine glycoside hydrolases and inexpensive donors such as maltose or xylan, access to mono-alpha-glucoside or mono-beta-xyloside of 9-fluorenylmethanol was obtained. Additionally, interesting polyglycoside derivatives were isolated. Biological testing indicated that in vitro treatment with these carbohydrate derivatives may influence the balance of cytokines in the environment of human peripheral blood mononuclear cells (PBMC), restricting the harmful effect of herpes simplex type 2 replication. In fact, these carbohydrate derivatives tested in WISH cells did not show any significant antiviral activity.
[Show abstract][Hide abstract] ABSTRACT: In pursuing a research on the antiviral and immunomodulatory activity of tilorone congeners, two new series of compounds were prepared and pharmacologically explored: 9-fluorenone carboxyhydroxyesters, indicated as AG, and 9-fluorenone carboxyhydroxamides, indicated as MG. Two of them, AG17 and MG3, were used as sugar acceptors in the transglycosylation reactions performed by alpha- and beta-glucosidases extracted from the marine mollusc Aplysia fasciata providing different alpha- and beta-, mono- and oligosaccharides. Then aglycons and saccharides were assayed for cytotoxicity, for anti-herpes virus-2 properties on peripheral blood mononuclear cells (PBMC) and for their capability to trigger human cells to produce antiviral cytokines such as IFNalpha and TNFalpha. Some promising compounds were individuated whereas the utility of the biocatalytic procedures in the preparation of pure anomeric material was further focused.
No preview · Article · Mar 2008 · European Journal of Medicinal Chemistry
[Show abstract][Hide abstract] ABSTRACT: Ornithine transcarbamoylase from ovine liver has been purified to homogeneity. Like all anabolic OTCs, the ovine enzyme is a trimer, constituted by identical subunits of 34 kDa. Sequence analysis of the 54 N-terminal residues of ovine OTC shows a high degree of homology with the human enzyme. The optimum pH and the Michaelis constants for the catalytic reaction were determined. The ovine enzyme is the most thermostable one among mammals OTCs, its critical temperature being 6 °C higher than those measured for the other enzymes. The enzyme has been crystallised and the structure determined at 3.5 Å resolution. Crystals belong to the cubic P4332 space group, with a
= 184.7 Å and a solvent content of about 80%. There is no evidence of any ligand in the active site cavity, indicating that the crystals contain an unliganded or T state of the enzyme. The unliganded OTCase enzyme adopts a trimeric structure which, in the crystal, presents a three-fold axis coincident with the crystallographic one. The conformation of each monomer in the trimer is quite similar to that of the liganded human protein, with the exception of a few loops, directly interacting with the substrate(s), which are able to induce a rearrangement of the quaternary organisation of the trimer, that accounts for the cooperative behaviour of the enzyme following the binding of the substrates.
[Show abstract][Hide abstract] ABSTRACT: Single cell protein (SCP) and crude pectinolytic enzymes production from citrus pulps is reported. SCP and enzymes were produced by slurry-state flask cultivation of Aspergillus niger and Trichoderma viride on pulps from lemon juice clarification. Production as well as crude pectinase activity was not affected by the high dry matter content of the pulps. Both the protein content in the residue and the enzyme activity in the supernatant were higher in T. viride than in A. niger culture. The crude pectinase of T. viride, whose specific activity was similar to that found for a commercial concentrated preparation, could be utilized in the same citrus processing factory as well as in other factories which use large amounts of pectinolytic crude preparations, for example to enhance depuration plant performance.
[Show abstract][Hide abstract] ABSTRACT: Extracts of ripening olive fruits (Olea europaea L. cv. Kalamata) -were analyzed for the presence of lipoxygenase activity and for the content of phenolic compounds, which are lipoxygenase inhibitors. Two distinct lipoxygenase activities were identified by their pH optima and sensitivity to the inhibitor nordihydroguaiaretic acid (NDGA). Both activities were low during early ripening stages, and increased sharply between 57 and 94 days postanthesis, reaching a plateau at about 120 days. The content of phenolic compounds, mainly oleuropein, changed in the opposite way, suggesting their involvement in the regulation of the two lipoxygenase activities during the olive fruit development. The two lipoxygenase activities could have a role in fruit maturation and senescence.
No preview · Article · Oct 2000 · Journal of Food Biochemistry
[Show abstract][Hide abstract] ABSTRACT: Human liver ornithine carbamoyltransferase undergoes absorbance changes in the UV region upon formation of the carbamoylphosphate-norvaline-enzyme ternary complex. The UV changes are similar in the presence of carbamoylphosphate alone, whilst they are lower in the presence of ornithine or norvaline alone. The extent of the UV changes correlates with the enzyme susceptibility to proteolytic degradation. The free native enzyme is completely and rapidly hydrolyzed by trypsin, whilst it is partially protected upon carbamoylphosphate binding. The extent of protection increases for the carbamoylphosphate-norvaline-enzyme ternary complex. These results strongly suggest that the binding of the first substrate, i.e. carbamoylphosphate, to human ornithine carbamoyltransferase induces a large protein isomerization, which regards the polar domain plus a part of equatorial domain of each subunit.
Preview · Article · Jul 1999 · Biochemistry and molecular biology international
[Show abstract][Hide abstract] ABSTRACT: A quantitative ultraviolet detection method for determining ornithine transcarbamylase (OTC-ase) activity using micellar electrokinetic chromatography (MEKC) is described. The method is based on the direct determination of citrulline formed upon enzymatic reaction. Using a background electrolyte consisting of 35 mM sodium tetraborate, pH 9.3, containing 65 mM sodium dodecyl sulfate (SDS), the peak of citrulline in the electropherogram was easily identified and integrated. This allowed us to determine the rate of formation of the reaction product and to calculate the kinetic parameter Km of the OTC-ase investigated. The capillary electrophoretic method developed was applied to the determination of OTC-ase activity in plasma samples for citrulline in the nanogram range.
[Show abstract][Hide abstract] ABSTRACT: Treatment of ornithine carbamoyltransferase from dolphin Stenella with pyridoxal phosphate, followed by reduction with NaBH4 resulted in complete loss of enzyme activity. The phosphate alone or the substrate analogue 2-aminovaleric acid moderately decreased the extent of inactivation, while carbamoyl phosphate plus 2-aminovaleric acid provided complete protection from inactivation. The partially inactivated enzyme showed K(m) values for substrates equivalent to those of native enzyme and lowered Kcat values. Two lysyl residues were substantially modified in the absence of ligands but only one of them was responsible for the inactivation of catalytic activity. Modification of a single subunit was sufficient to completely abolish the catalytic activity of the trimeric enzyme. The lysine involved has been identified as lysine 56 on the known primary structure of homologous human liver enzyme.
Full-text · Article · Aug 1996 · European Journal of Biochemistry
[Show abstract][Hide abstract] ABSTRACT: 1. Ornithine carbamoyl transferases from liver of the dolphin Stenella and the shark Sphyrna zygaena were purified to homogenity and compared for some kinetic and structural properties. 2. The two enzymes showed a specific activity of 211 and 115 respectively. 3. With respect to molecular weight, trimeric subunit structure and Km values, they were alike and similar to enzymes from other species. 4. Both enzymes were thermolable, but they were protected from thermal inactivation in a different way by ornithine and phosphate. 5. The two enzymes focused, respectively, at pH 8.6 and between pH 6.4 and 8.0, the former value being appreciably higher than those of enzymes from other species.
No preview · Article · Jul 1993 · Comparative biochemistry and physiology. B, Comparative biochemistry
[Show abstract][Hide abstract] ABSTRACT: Ornithine carbamoyltransferase (carbamoylphosphate: L-ornithine carbamoyltransferase, EC 184.108.40.206) has been partially purified from C.limonum leaves. The data indicate the presence of only the anabolic enzyme. The activity is strongly influenced by pH, ionic strength and ornithine concentration. Optimal activity for the enzyme dissolved in the tri-buffer: diethanolamine,2-(N-morpholino) ethanesulfonic acid, N-ethylenmorpholine (0.051 M/0.1 M/0.051 M) is at pH 9.0, when ornithine is 10 mM. The enzyme catalyses an ordered-sequential process in which carbamoyl phosphate binds first followed by L-ornithine and then L-citrulline leaves followed by phosphate. Support for this statement comes from product inhibition and evidence of abortive ternary complex formation.
No preview · Article · Mar 1993 · Biochemistry and molecular biology international