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R A Usmanov

Publications and source records attributed to R A Usmanov.

17 recordsLinked to original sources
PubMed1996

Interaction of dihydroxyethylthiamine pyrophosphate with transketolase.

Deprotonated form of dihydroxyethylthiamine pyrophosphate (DHETPP) is an intermediate product of the transketolase reaction. We have shown that when added to the reaction medium DHETPP can act as a substrate of the holoenzyme. The rate of the enzymatic reaction is quite close to that observed with ordinary substrates of transketolase. This fact suggests that the interaction of DHETPP with the holotransketolase and its deprotonation are not rate-limiting steps of the transketolase reaction.

Apoenzymes↗
PubMed1995

[Enzymatic synthesis of dihydroxyethylthiamine pyrophosphate, its optical characteristics, and quantitative determination].

Modification of the method of Holzer et al. for the synthesis and purification of dihydroxyethylthiamine pyrophosphate, an intermediate of the transketolase reaction, is described. Absorption and circular dichroism spectra as well as the molar coefficient of circular dichroism absorption at 273 nm are presented. A convenient and rapid procedure for quantitative determination of dihydroxyethylthiamine pyrophosphate in solution where it is present as the only component or as a mixture with thiamine pyrophosphate (or other optically inactive compounds), is proposed.

Animals↗
PubMed1995

Quantitative determination of dihydroxyethylthiamine pyrophosphate by the circular dichroism method.

This work is concerned with a convenient and fast method for quantitative determination of dihydroxyethylthiamine pyrophosphate in solution where it is present as the only component or as a mixture with thiamine pyrophosphate (or other optically inactive compounds). The molar coefficient is given for circular dichroism absorption of dihydroxyethylthiamine pyrophosphate. The method for determining thiamine pyrophosphate in the presence of dihydroxyethylthiamine pyrophosphate is described as well.

Anion Exchange Resins↗
PubMed1985

The effect of thiamine pyrophosphate modification on its coenzyme function in a transketolase-catalyzed reaction.

The coenzyme function of TPP analogues: 4'-NH-methyl-TPP,6'-methyl-TPP and 6'-methyl-4-nor-TPP has been studied in a transketolase-catalyzed reaction. Their dissociation constants have been found with the aid of the circular dichroism method, and coenzyme activity has been determined in a complete transketolase reaction, involving the substrate-donor and the substrate-acceptor, and also at the intermediate stage (by the alpha-carbanionic intermediate oxidation rate). The coenzyme activity values have been found different and largely dependend on the nature of the substrates used. A possibility of TPP functioning by the "two-center mechanism" in a transketolase-catalyzed reaction is discussed.

Kinetics↗
PubMed1983

[Function of the arginine residue in the active center of baker's yeast transketolase].

The binding of anionic and non-anionic donor substrates to baker's yeast transketolase modified at the arginine residue by 2,3-butanedione was studied. The modified enzyme binds two thiamine pyrophosphate molecules per mole of protein, forms a complex with a charge transfer as recorded by circular dichroism (CD) spectra and retains its ability to bind anionic and non-anionic substrates. The values of the binding constants as determined from the CD spectra remain either unchanged or are changed very slightly. The values of the kinetic parameters, Km and V, for the transketolase-catalyzed oxidation reaction in the presence of anionic and non-anionic donor substrates were calculated. The Km values for both substrate groups were not affected by the enzyme modification, while those of V were decreased 5-10 times. The experimental data suggest that the arginine residue is not involved in the enzyme binding to the substrates but is catalytically essential.

Arginine↗
PubMed1983

Interaction of baker's yeast transketolase modified by 2,3-butanedione with anionic and nonanionic substrates.

Baker's yeast apotransketolase modified by 2,3-butanedione binds thiamine pyrophosphate, a coenzyme of transketolase, and forms a charge transfer complex which can be identified by the CD spectrum. The enzyme retains thereby its ability to bind anionic and nonanionic substrates. The affinity of the modified enzyme for donor substrates changes insignificantly, whereas Vmax decreases 5-10-fold. The results of the study show that, although the arginine residue of the active center is not involved in substrate binding, it is essential for catalysis.

Anions↗
PubMed1978

[Study of different conformational states of transketolase by the method of perturbation UV-spectrophotometry].

The conformational parameters of apotransketolase, holotransketolase and the enzyme-substrate complex were studied using colvent perturbation technique, a 20% solution of dimethyl sulfoxide being used as perturbant. The apoenzyme was found to contain 4--5 tryptophane residues and 12--14 tyrosine residues accessible for the solvent. The amount of the residues is reduced nearly 2-fold after formation of the holoenzyme. In the enzyme-substrate complex the amount of tryptophane and tyrosine residues accessible for the solvent is increased up to the inital value. The changes in the conformational states of the active site of apoenzyme, holoenzyme and the enzyme-substrate complex are discussed.

Anilino Naphthalenesulfonates↗