Effects of thiamine deficiency and thiamine administration on the thiamine diphosphate-dependent enzymes in rat liver.

Abstract

Rats were made deficient by thiamine deprivation and the enzyme activities of α-keto acid dehydrogenases and transketolase were measured with or without addition in vitro of thiamine diphosphate in liver mitochondria and in supernatants of liver homogenate, respectively.The activities of pyruvate and 2-oxoglutarate dehydrogenases were determined by a spectrophotometric method according to Massey, that of transketolase determined by Racker's method. The values of enzyme activity as well as the thiamine contents in the preparations were compared with those of the animals whose deficiencies were restored by thiamine administration. The thiamine deprivation resulted in a significant decrease of these enzyme activities accompanied with the decrease of thiamine contents. However, the α-keto acid dehydrogenase in liver mitochondria of deficient rats were almost restored to normal levels by an in vitro addition of thiamine diphosphate to the enzyme reaction mixture, while the restoration of transketolase in the supernatant of liver homogenate was not observed by the addition in vitro of thiamine diphosphate. This would suggest a decrease of apoenzyme of transketolase caused by thiamine deficiency in contrast to those of α-keto acid dehydrogenase.These findings reflect to the results that only once administration of thiamine, in vivo, caused a prompt restoration of α-keto acid dehydrogenase, while the restoration of transketolase was not sufficient with once administration of thiamine in spite of the rapid recovery of thiamine contents. The restoration of transketolase needed a prolonged administration of thiamine to return to normal levels. On the other hand, thiamine deficiency had no effect on the thiamine diphosphate-independent enzyme, thiamine pyrophosphokinase, as shown in the fact that the decreased thiamine contents in enzyme extracts returned promptly to normal by thiamine administration. And also a large dose administration of thiamine to normal rats caused no induction of the thiamine diphosphate-dependent enzymes.