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[Niacin deficiency and correlation between oxidative reactions of the pentose phosphate pathway of carbohydrate metabolism and transketolase activity].

Rat were kept on the niacine-deficient diet with addition of excess L-leucine. This led to an appreciable reduction of the level of all the forms of nicotinamide coenzymes in the liver, heart, brain and blood, as well as to the loss of niacine function (as coenzyme) in dehydrogenase reactions in the test tissues. The increase in the glucose-6-phosphate level in the heart dependent on changes in the activity of glucose-6-phosphate dehydrogenase. The keeping on the diet devoid of niacine was followed by activation of blood transketolase and by transition of the biosynthesis of pentosophosphates from the oxidative to the non-oxidative branch of the pentosophosphate pathway. Administration of 3-acetylpyridine to both intact and avitaminotic rats revealed vitamin action of the preparation on the level of nicotinamide coenzymes and the activity of NADP-dependent dehydrogenase and showed that 3-acetylpyridine is not fit as antivitamin for use with a purpose of aggravating niacine deficiency in rats under the experimental conditions described.

Animals↗
PubMed1980

[Determination of half-life time for the key enzymes of the pentose phosphate pathway--glucose-6-phosphate dehydrogenase and transketolase].

Using hormonal induction by thyroxin, the half-life time and the rate constants for the synthesis and degradation of glucose-6-phosphate dehydrogenase and transketolase were determined. It was shown that the mechanisms of activation of these enzymes by thyroxin are different. Under hyperthyrosis an increase in the activity of glucose-6-phosphate dehydrogenase is induced by a decrease (2-fold) of the degradation rate constant; the rate constant of synthesis is not changed thereby, while the half-life time for the enzyme increases 2-fold. The activation of transketolase in this case can be accounted for by an almost 1,5-fold increase in the rate of the enzyme synthesis, whereas the degradation rate constant and the half-life time of the enzyme remain practically unchanged.

Animals↗