Abstract
It has been reported that some vitamins besides their function as coenzyme regulate the enzyme activity by induction (coenzyme induction) or repression (coenzyme repression) of the enzyme proteins. In this paper, the activity changes of pyruvate and 2-oxoglutarate dehydrogenases with thiamine contents were examined by using Escherichia coli. When a Hfr strain (KG 33) derived from E. coli K 12,auxotrophic for thiazole was grown overnight in Davis medium containing minimal concentration (10-^8M) of thiamine for growth, bacterial thiamine content of the mutants was about one fifth of that of the parent and its α-keto acid dehydrogenase activities were fairly low as compared with that of the parent. The addition of thiamine diphosphate to a reaction mixture of the enzyme extracted from the mutant restored the dehydrogenase activity to the extent of the enzyme extracted from the parent or the mutant grown with excess thiamine (10-^6M). Similar results were obtained with a mutant (KG 674) of E. coli K 12,auxotrophic for thiamine. Elevation of thiamine contents in E. coli K 12 by adding thiamine (10-^6M) or phenylalanine (10-^2M) in the growth medium caused no increase of the dehydrogenase activity as compared with the bacteria grown without adding the compounds. These results suggested that the synthesis of apoenzymes was neither impaired by thiamine depletion nor induced by excess thiamine in the cells. Extensive dialysis of the enzyme extract from the mutant grown on thiamine minimum caused to decrease the dehydrogenase activity without change of thiamine content, while the same treatment of the enzyme extract from the mutant grown on excess thiamine had no effect on enzyme activity but decrease on thiamine content in the extract. (Received Nov. 25,1970)
