Abstract
The action of oxythiamine on yeast changed from inhibitory to stimulatory at a certain stage of incubation. In this case disappearance of oxythiamine and increase of thiamine were proved by paper ionophoresis and chemical assay. Simultaneous addition of the pyrimidine moiety of thiamine with oxythiamine caused a considerable decrease of the decomposition of the antagonist and an increase of the vitamin synthesis. Oxythiamine, also, exhibited almost the same effect on E. coli thiazole-less mutant as thiamine and its thiazole-moiety, while the antivitamin had no effect on pyrimidine-less mutant. In the incubation products of oxythiamine with washed cells of yeast or E. coli, the occurence of the pyrimidine and thiazole moieties of oxythiamine was demonstrated by paper chromatography and paper ionophoresis. From these results it is considered that oxythiamine is cleaved to its two moieties and the thiazole part is utilized as a precursor of thiamine. However, oxythiamine and its pyrimidine moiety, respectively, exerted a growth effect on E. coli thiamine-less and pyrimidine-less mutants after 15 hours'lag period. In these mutants transformation of 4-hydroxyl group of pyrimidine to amino group is supposed.
