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Z V Gorbach

Publications and source records attributed to Z V Gorbach.

At least 19 recordsLinked to original sources
PubMed1990

[Regulation of gluconeogenesis in the liver of vitamin B1-deficient rats].

Radiometric assays revealed that thiamine deficiency in rats to whom hydroxythiamine was administered in variable doses, is concomitant with activation of gluconeogenesis from pyruvate in liver tissue. The most probable mechanism of this effect is the cAMP-dependent activation of key enzymes of intracellular glucose synthesis. This process is facilitated by the diminution of the ratio of free forms of NAD+ and NADPH in the cytoplasm.

Alanine Transaminase↗
PubMed1989

[A method of determining the concentration of thiamine].

The rate of the production of thiazole, the first product of the reaction, catalyzed by thiaminase I (EC 2.5.1.2) from Anodonta cygnea muscles is characterized by an initial flash-up explained by a considerable difference in the rates of the enzyme-substrate complex formation and its further transformation. Basing on this phenomenon, a new method for measuring the total thiamine in vitro and in biological material has been developed. Optimal conditions for thiamine measurements in the blood and urine have been selected.

Animals↗
PubMed1989

[Kinetic properties of transketolase from the rat liver in a reaction with xylulose-5-phosphate and ribose-5-phosphate].

An analysis of steady-state kinetics of purified rat liver transketolase shows that the reaction proceeds according to a two-stroke substitution ("ping-pong") mechanism. Based on the kinetic data, a competitive relationship was shown to exist between xylulose-5-phosphate and ribose-5-phosphate for the sites of substrate binding by the substituted form of the enzyme with the formation of a non-productive abortive complex (kd = 125 microM). The values of constants of two monomolecular steps of the reaction (k2 = 42 s-1; k4 = 9.4 s-1) were determined. It was assumed that the maximum rate-limiting step of the transketolase reaction is the degradation of the substituted form of transketolase--ribose-5-phosphate complex having a rate constant of k4.

Animals↗
PubMed1987

[Characteristics of intracellular metabolism of carbohydrates and amino acids in animals with thiamine deficiency].

Vitamin B1 deficiency in mongrel albino rats induced by oxythiamine is concomitant with an increase in the ratio of free forms of NAD+/NADH, NADP+/NADPH in liver mitochondria. This is accompanied with a rise in steady-state concentrations of isocitrate, 2-oxoglutarate and with a decrease of malate in liver tissue, which testifies to the prominent regulatory role of the 2-oxoglutarate dehydrogenase complex in the intracellular metabolism under vitamin B1 deficiency. Moderate physical load causes a 10-fold increase in the steady-state concentration of pyruvate and lactate in the blood of thiamine-deficient animals, which seems to be due to the stimulation of glycolysis in the maintenance of energy homeostasis. The observed increase in the excretion of pyruvate, lactate, 2-oxoglutarate (30-fold against control) and pentose phosphates (3-fold) with urine, depending on the degree of vitamin B1 deficiency, points to one of essential mechanisms of cell metabolism stabilization under the given pathological condition.

Acetone↗
PubMed1986

[Metabolism of transketolase coenzyme in the rat liver].

Kinetic analysis permitted to determine two sites of hydroxythiamine diphosphate binding in apotransketolase. The Ki values for these sites differed significantly: (7-22) X 10(-9) M and (13.0-19.7) X 10(-8) M. The rate of thiamine diphosphate turnover within holotransketolase in rat liver tissue was studied by the radioisotope method, using [14C]thiamine as a labeled precursor. The absolute values of half-substitution time and the rate constant of coenzyme degradation in the transketolase molecule are close to those for the protein moiety of the enzyme and are 153 hours and 0.108 days-1, respectively. In vivo rat liver transketolase exists in a substituted alpha-carbanion form. Within the holoenzyme molecule substitution of thiamine diphosphate for hydroxythiamine diphosphate does not influence the formation of an intermediate alpha-carbanion form of the enzyme.

Animals↗
PubMed1985

[Characteristics of carbohydrate metabolism in the rat liver in thiamine deficiency].

Thiamine deficiency in rats induced by oxythiamine is accompanied by an increase in the free NADP+/NADPH ratio in liver tissue, which results in multifold stimulation of the metabolite flux in the oxidation branch of the pentose cycle. The increase in the intracellular concentrations of isocitrate and alpha-ketoglutarate with a simultaneous decrease of malate in the liver of vitamin-deficient rats points to the inhibition of alpha-ketoglutarate dehydrogenase responsible for the anomalous metabolism under conditions of thiamine deficiency. The decrease of the functional activity of the tricarboxylic acid cycle is concomitant with the activation of conversions in the oxidation branch of the pentose cycle, glucuronate and glycolytic pathways of carbohydrate metabolism, which is directed at eliminating the energy deficiency in rats with B1-hypovitaminosis.

Animals↗
PubMed1983

[Peculiarities of carbohydrate metabolism in the rat liver due to the limited accessibility of thiamine].

It was found that the progressive development of vitamin B1 deficiency in rats caused by varying doses of oxythiamine results in a sharp decrease of the free NAD/NADH ratio in the liver after injection of a high dose of the antivitamin. The value of this ratio was calculated from the intracellular concentrations of pyruvate, lactate and Keq for lactate dehydrogenase, whose activity remained practically unchanged throughout the experiments. The increase of the cAMP level in the liver caused by corresponding doses of oxythiamine was concomitant with a marked activation of cAMP-dependent processes.

Adenine Nucleotides↗
PubMed1982

[Purification and some properties of molecular forms of 6-phosphogluconate dehydrogenase from rat liver].

Using stepwise protein fractionation by (NH4)2SO4 and ion-exchange chromatography on CM-cellulose, DEAE-cellulose and SP-Sephadex, two isoforms of 6-phosphogluconate dehydrogenase, A and B, from rat liver were obtained. The method developed allows to achieve complete separation of these forms and to obtain preparative amounts of the protein with specific activities of 5.7 and 10.7, respectively. The native enzyme forms A and B have molecular weights of 107000 and are represented by dimers composed of subunits with identical molecular weights equal to 54000. Both isoforms have a pH optimum at 8.5 and reveal different sensitivity to MgCl2 and MnCl2. The tetrahedron-shaped ions (phosphate, molibdate, arsenate) inhibit the both molecular forms of the enzyme, The Arrhenius plots for the reaction rate are uninterrupted lines within the temperature range of 21-44 degrees; the values of activation energy and the temperature coefficient for isoforms A and B are 12750 and 13500 cal/mole and 2.05 and 2.15, respectively.

Animals↗
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↗
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↗
PubMedDate not supplied

[Kidney sorbitol dehydrogenase: kinetic mechanism].

Properties of sorbitol dehydrogenase isolated from rat kidney were studied. Sorbitol dehydrogenase reactions followed the consecutive irregular order as shown in studies of kinetic patterns, inhibition by end products and thermoinactivation of the enzyme in the presence of substrates.

Animals↗
PubMedDate not supplied

[Isoenzyme spectrum and kinetic properties of pyruvate kinase from the liver of thiamine-deficient rats].

Thiamine-deficiency in animals induced by everyday subcutaneous administration of oxythiamine in a dose of 4, 40 and 100 mg/kg of weight for 10 days results in a decrease of the total activity of pyruvate kinase in the liver tissue and does not affect the mentioned index in the kidney and heart tissues. It is shown that as a result of the enzyme fractionation in the column with DEAE-cellulose the total activity of pyruvate kinase in the liver tissue of rats with thiamine-deficiency decreases due to L-isoform while the content of M-isoform remains unchanged. Thiamine deficiency does not affect kinetic characteristics of the L-isoform, extracted from the liver and this shows the absence of changes in the degree of phosphorylation of pyruvate kinase L-isoform under these conditions.

Animals↗
PubMedDate not supplied

[Stimulation of nucleic acid biosynthesis by phosphopentoses].

Phosphopentose stimulation of nucleic acids biosynthesis for 3h after subcutaneous phosphopentose administration in doses of 18 and 27 mg per rat has been stated. Injections of phosphopentoses (ribose-5-phosphate, xylulose-6-phosphate, ribulose-5-phosphate in the ratio of 1.0:0.3:0.3) were followed by a two-fold increase in the rate of [2-14C] orothic acid incorporation into cytoplasmic RNA of the rat liver. It is supposed that rapidly exchanging types of RNA contribute most of all to the effect of the label incorporation increase and the stimulation mechanism is associated with a rise of phosphoribosyl pyrophosphate accessibility as a substrate and an allosteric regulator of key enzymes of the synthesis of purine and pyrimidine nucleotides.

Animals↗
PubMedDate not supplied

[Characteristics of the products of thiamine degradation by molluskan thiaminase I].

Tiaminase I (EC 2.5.1.2) catalyzed degradation of thiamin in the reaction mixture free of substrate-acceptor. Thiamin exhibited properties of both substrate-donor and -acceptor of the group transferred by thiaminase I. Identification of the products developed after thiaminase reaction involving thiamin was performed using chromatography and radiometry. Kinetics of the reaction is discussed.

Alkyl and Aryl Transferases↗