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Iu M Ostrovskiĭ

Publications and source records attributed to Iu M Ostrovskiĭ.

At least 37 records · Page 2Linked to original sources
PubMed1981

[Purification and properties of rat liver transketolase].

Transketolase was isolated from wet tissue of rat liver and purified by ammonium sulfate and CM-cellulose fractionation and by adsorption chromatography on hydroxylapatite. The native enzyme is made up of two subunits with molecular weight of 70 000, is electrophoretically homogeneous and has a specific activity of 2.8 u. per mg of protein (30 degrees). The enzymatic and fluorimetric assays revealed the presence of two moles of thiamine diphosphate per mole of protein. The Arrhenius plots for the rate of the transketolase reaction with a pentose phosphate mixture as substrate are continuous at 10-32 degrees; the activation energy is 89.9 cJ/mole, temperature index is 3.3. The curve for the reaction rate versus substrate concentration is S-shaped; the apparent Km value for xylulose 5-phosphate is 2.2 x 10(-5) M. The ions with a tetraedric structure (arsenate, phosphate, sulfate) act as competitive inhibitors of the transketolase-catalyzed reaction.

Animals↗
PubMed1980

[Direct measurement of the antivitamin action of parenterally injected thiaminase].

Thiaminase (EC 2.5.1.2) from freshwater bivalve molluscs is a polycosubstrate enzyme, which is resistant to temperatures below 55 degrees. The activation energy of the enzyme with cystein is 15077 cal/mole, with aniline--15948 cal/mole. Thiaminase when injected parenterally to albino mice 2 hrs after injection of [2-14C]thiamine causes an extensive destruction of labelled vitamin b1, which is evidenced from the [14C]thiazole content in urine, liver and kidneys. The total radioactivity and the content of [14C]thiazole in the urine samples collected within 6 hrs after thiamine injection are increased. Cysteine and histidine in combination with thiaminase have no activating effect similar to that observed "in vitro". In the experimental series when non-labelled vitamin B1 from animal tissues (liver, kidney, spleen, muscle) was substituted by the labelled one, the parenterally injected enzyme destroyed up to 30-50% of total thiamine content. Brain and skeletal muscle tissues are more resistant to thiaminase action.

Alkyl and Aryl Transferases↗
PubMed1979

[Tumor and body interrelationships in 14C-thiamine utilization].

Variations in the content of 14C-thiamine, thiamine-dependent enzyme transketolase (TK), and thiamine diphosphate (TDP) in mouse tissues were studied during Ehrlich's ascites tumour growth. The concentration of TDP in the liver of tumour-bearing animals continuously drops during 10 days after inoculation, TDP level in the tumour itself decreases more abruptly by the terminal period of tumour growth (the 10th day). At the same time the tumour demonstrates sharp deficiency of the coenzyme and redundance of apoenzymatic forms of TK. The growing deficiency of thiamine in the tumour favours greater tension of thiamine metabolism and appearance of competitive tumour-host interrelationships that are most pronounced in the presence of hypovitaminosis.

Animals↗
PubMed1978

[Kinetic characteristics of thiamine diphosphate biosynthesis by thiamine pyrophosphokinase from rat liver].

The kinetic analysis of bisubstrate enzymatic reaction catalysed by electrophoretically homogenous thiamine pyrophosphokinase (EC 2.7.6.2), isolated from rat liver has been carried out. Kinetic studies of the initial rates in the absence of the products and inhibition by the reaction products as well as the data from the equilibrium dialysis suggest that the reaction proceeds through the formation of a ternary enzyme-substrate complex. The combination with substrates and release of the products appears to be highly ordered. A possible scheme of the reaction mechanism is discussed.

Animals↗
PubMed1978

[Free amino acid concentration in the tissues of rats with different forms of thiamine deficiency].

The levels of free amino acids in rat tissues under thiamine deficiency induced by antivitamin (oxithiamine) and under thiamine-deficient diet were studied. Changes in the amino acid pool at these two forms of vitamin B1 deficiency were revealed. The most typical change consists in extensive accumulation of alanine and glutamate with a simultaneous decrease in the amount of many other essential and non-essential amino acids. The disturbances in the amino acid pool under thiamine deficiency may be probably regarded as resulting from inhibition of alpha-keto acid dehydrogenase activities.

Amino Acids↗
PubMed1977

[Biosynthesis of mitochondrial protein in rat liver under conditions of vitamin B 1 deficiency following oxythiamine injection].

The incorporation of labelled precursors into mitochondrial proteins of liver under different duration of oxythiamine (antivitamin B1) effect was studied in the whole organism and in a cell-free system. After 24 hrs following the injection, oxythiamine at a dose of 400 mg/kg of body weight increases the mitochondrial protein synthesis in vivo without changing the protein-synthesizing capacity of isolated mitochondria. After 72 hrs following the injection of the same dose of preparation, a sharp increase in the rate of protein label incorporation into the mitochondria was observed. The protein synthesis in mitochondria in the whole body studies also showed an increase. It is assumed that oxythiamine enhances the inductive synthesis of mitochondrial thiamine phosphate-dependent enzymes or activates the syntheses of other enzymic systems, capable of increasing the utilization of alpha-keto acids accumulated under conditions of thiamine deficiency.

Animals↗
PubMed1977

[Possible mechanism of action of oxythiamine on nucleic acid metabolism].

Hydoxythiamine injections (400 mg/kg for 72 hours) resulted in the inhibition of transketolase activity and of 14C-orotic acid incorporation into RNA in rat liver tissue. At the same time, the decrease of RNA and phosphoribosylpyrophosphate levels has been observed, which suggests a regulation effect (via pentospohosphates) of hydroxythiamine on nucleotide and nucleic acid metabolism.

Animals↗