[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.