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Biomedical subjects

V M Belikov

Publications and source records attributed to V M Belikov.

At least 19 recordsLinked to original sources
PubMed2000

Interaction of tyrosine phenol-lyase with phosphoroorganic analogues of substrate amino acids.

The phosphinic analogues of tyrosine and pyruvate were first demonstrated to be substrates in the reactions of elimination and synthesis catalyzed by tyrosine phenol-lyase. Kinetic parameters of the enzymatic process were determined, and the first enzymic synthesis of an aminophosphinic acid was carried out. Replacement of the planar HOOC-group by the tetrahedral (HO)(O)PH-group in the substrate slightly affected its affinity for the enzyme but substantially diminished the conversion rate. For phosphonic analogues, containing (HO)2(O)P group, the affinity to the enzyme was decreased considerably while the conversion was completely prevented. Thus, the structural parameters of the acid group are important not only for the affinity for the enzyme, but also for the formation of the catalytically competent conformation of the active site.

Amino Acids↗
PubMed1995

2-Methyl-L-tryptophan is a substrate of tryptophanase.

Tryptophanase was generally considered to be inactive towards tryptophan derivatives substituted at 2-position of the indole ring. We have shown that cells containing tryptophanase catalyze the formation of 2-methyl-L-tryptophan from 2-methylindole and L-serine, and from 2-methylindole, pyruvate and ammonium ion. The kinetics of pyruvate formation from 2-methyl-L-tryptophan and its alpha-deuterated analogue catalyzed by homogeneous tryptophanase were examined. The primary deuterium isotope effect (kH/kD = 4.0) as well as the absorption spectrum of tryptophanase complex with 2-methyl-L-tryptophan indicate that the rate of enzymatic reaction of 2-methyl-L-tryptophan is in a considerable degree determined by the stage of removal of alpha-proton.

Absorption↗
PubMed1994

Tryptophanase from Escherichia coli: catalytic and spectral properties in water-organic solvents.

In water-methanol and water-dimethylformamide (DMF) (1:1 v/v) solutions tryptophanase from E.coli retains its abilities to form a quinonoid complex with quasisubstrates and to catalyze the decomposition of S-o-nitrophenyl-L-cysteine (SOPC). Both the KM and Vmax values decrease in water-organic media. The affinities of tryptophanase for L-alanine, L-tryptophan, oxindolyl-L-alanine and indole in aqueous methanol are decreased, the effect being stronger for the more hydrophobic substances. In a water solution tryptophanase catalizes the reaction of SOPC with indole to form L-tryptophan while in water-organic solvents only decomposition of SOPC is observed.

Alanine↗
PubMed1990

[Catalytic properties of E. coli tryptophanase in a 50% aqueous solution of methanol and dimethylformamide].

Tryptophanase from E. coli retains its ability to form quinonoid intermediate with L-alanine in water--methanol and water--dimethylformamide (1:1 v/v) solutions. Under these conditions the enzyme catalyzes decomposition of S-o-nitrophenyl-L-cysteine (SOPC) to o-nitrophenylthiol, pyruvate and ammonium ion. The enzyme's affinity for this substrate increases on going from water to water-organic solvents whereas the reaction rate decreases. In 50% methanol tryptophanase catalyzes the formation of L-tryptophan from indole and SOPC; in the mixture of 2H2O and C2H3O2H (1:1) the enzymatic isotope exchange of alpha-proton of L-phenylalanine with complete retention of configuration was observed.

Catalysis↗
PubMed1989

[Effect of enteral feeding on protein metabolism in patients with peritonitis].

Thirty patients with peritonitis of different etiology were examined. Deep alterations of protein metabolism were revealed resulting from dyscoordination of amino acid metabolism. Efficiency of unbalanced amino acid mixtures was shown and on the contrary, the absence of a therapeutic effect when using balanced mixtures.

Adolescent↗
PubMed1988

Tyrosine phenol-lyase from Citrobacter intermedius. Factors controlling substrate specificity.

L-Amino acids are competitive inhibitors of tyrosine phenol-lyase from Citrobacter intermedius. For non-branched amino acids the correlation exists between -RTlnKi and side-chain hydrophobicity. Aspartic and glutamic acids are anomalously potent inhibitors taking into account low hydrophobicity of their side chains. This suggests the presence of an electrophilic group in the active site which interacts with the terminal carboxylic group of aspartic or glutamic acids. Tyramine, beta-phenylethylamine and tryptamine do not display detectable inhibition. The esters and amides of aromatic L-amino acids, D-phenylalanine and D-tryptophan are competitive inhibitors. The enzymatic isotope exchange of the alpha-proton in 2H2O was observed only in the case of L-amino acids. For L-phenylalanine and L-tryptophan it was shown to proceed with complete retention of configuration. The substrate specificity of tyrosine phenol-lyase is controlled during the stage of phenol elimination. The OH group in the para position of the ring is necessary for this stage to proceed. The same stage is also sensitive to the steric parameters of the substituent in the ring which ensures the second factor of control. When all the requirements of substrate specificity are fulfilled (L-tyrosine, 3-fluoro-L-tyrosine), the 'key' phenol-elimination step is not the rate-limiting one, the reaction velocity being determined by the preceding alpha-proton abstraction.

Amino Acids↗
PubMed1987

Kinetic description of proteolysis. Part 3. Total kinetics of peptide bonds hydrolysis in peptide mixtures.

A theoretical analysis of the general kinetics of peptide bond hydrolysis in peptide mixtures has been carried out. It is shown that the equation for the hydrolysis rate must include ensemble-averaged values which change as functions during hydrolysis. Thus the problem of describing the hydrolysis is reduced to finding these functions. As an example of theoretical prediction for the behavior of the averaged functions the procedure of calculating the averaged constant of chymotrypsin substrate specificity as a function of the degree of hydrolysis is presented. The analysis performed enables to find factors responsible for the decrease of hydrolysis rate, in particular, the role of the substrate specificity range and the S/E ratio. The design of specific experiments making it possible to measure the averaged values in the course of hydrolysis has been considered.

Chymotrypsin↗
PubMed1987

Kinetic description of proteolysis. Part 4. Hydrolysis kinetics of partial protein hydrolysates.

This report presents experimental data on kinetics of casein hydrolysate hydrolysis. The experiments were interpreted in the framework of a theory reported, which is guided by an experimentally measurable value--a total molar concentration of all peptides and amino acids (total amino nitrogen). The total amino nitrogen N was determined by photometry of N-trinitrophenyl (N-TNP) derivatives obtained by means of trinitrobenzenesulfonic acid (TNBS). Unlike the procedures reported previously, we stopped the proteolysis reaction by boiling, and performed the trinitrophenylation in a 20% V. aqueous solution of MeCN.

Amines↗
PubMed1986

Plasteins. Their preparation, properties, and use in nutrition.

The theoretical and practical aspects of the plastein reaction, which consist in the formation of a gel following the addition of an endopeptidase to a concentrated solution of a partial protein hydrolysate, are examined and the properties and possibilities of using plasteins in nutrition are discussed. It is shown that valuable protein food products can be obtained with the aid of the plastein reaction from proteins with an unbalanced amino acid composition and from chemically synthesized amino acids. Other applications of plasteins in nutrition are discussed and the studies carried out hitherto on the mechanism and driving forces of plastein formation are considered.

Amino Acids↗
PubMed1986

Kinetic description of proteolysis. Part 1. Peptic hydrolysis of proteins isolated from chicken heart: optimization in terms of time and substrate concentration.

Simple equation for the total rate of proteolysis is proposed. The equation, based on the renal mechanism of proteolysis includes the substrate concentration and some functions of the degree of hydrolysis. These functions are experimentally determined in the case of peptic hydrolysis of chicken heart proteins. The integration of differential equation made it possible to describe the kinetics of the proteolysis in terms of substrate concentration, degree of proteolysis and reaction time. The kinetics of proteolysis does not obey the Michaelis-Menten law. The proposed way for mathematical modelling permits the optimization by productivity.

Animals↗
PubMed1986

Kinetic description of proteolysis. Part 2. Substrate regulation of peptide bond demasking and hydrolysis. Liquid chromatography of hydrolyzates.

Lower peptides and amino acids in hydrolyzates of casein obtained with protosubtilin were determined using high pressure liquid chromatography (HPLC). The dependences of product concentrations in hydrolyzates produced at different substrate concentrations on the degree of hydrolysis were obtained. With an increase of the substrate concentration the real type of proteolysis changes from "zipper" to "one-by-one". This result supports the assumption that the substrate proteolysis regulation is realized through the change in the ratio of the rates of peptide bond demasking to those of peptide bond hydrolysis.

Amino Acids↗
PubMed1984

[Isolation and properties of tyrosine phenol-lyase from Citrobacter intermedius].

A method for preparation of homogeneous tyrosine phenol lyase (EC 4.199.2) from Citrobacter intermedius has been developed. The cells were cultivated in the media with a view to obtain a cell culture with a high activity of tyrosine phenol lyase. The isoelectric point for the enzyme lies at pH 4.9. Tyrosine phenol lyase is strictly stereospecific: it catalyzes the formation of pyruvate only from L-tyrosine, but not from D-tyrosine. Kinetic studies showed that K+ and NH4+ cations are non-competitive activators of the enzyme (Ka = 3.57 X 10(-3) and 1.34 X 10(-4) M, respectively).

Chromatography, DEAE-Cellulose↗
PubMedDate not supplied

[Elimination of phenylalanine from amino acid mixtures obtained from yeast hydrolysates and autolyzates].

In order to obtain amino acid mixtures devoid of phenylalanine, adsorption of aromatic amino acids was studied during their chromatography on ion-exchange resin IA-Ip. When 40 g of the amino acid mixture were passed through 400 ml of the swollen ion-exchange resin, phenylalanine and tyrosine were eliminated and 67% of dry substance were yielded. Ion-exchange resin adsorbed phenylalanine and tyrosine could be regenerated. The use IA-Ip is advantageous as compared with that of ion-exchange resin Amberlite IR-45 and activated charcoal.

Adsorption↗