Abstract
Biosynthesis of thiamine Lrom 2-methyl-4-aminomethylpyrimidine (AMP) by Sacch. cerevisiae was greatly inhibited at the presence of phenylthiazinothiamine (PTT) but biosynthesis from 2-methyl-4-amino-5-hydroxymethylpyrimidine (OMP), instead of AMP, with PTT was shown to be nearly equal to that without PTT. Biosynthesis from OMP or AMP by crude enzyme from Sacch. cerevisiae, however, was proved to have no inhibition at the presence of PTT. AMP alone, when incubated with yeast cells, had been uptaken by cells from the medium more completely than OMP (this was proved by biosynthesis of thiamine with thiazole moiety by the washed cells after the incubation) . Addition of PTT to the medium was shown to give strong inhibition on uptake of AMP but practically no inhibition on that of OMP. It was suggested that the inhibitory effect of PTT on the biosynthesis of thiamine from AMP was due to the inhibition of incorporation of AMP to the yeast cells.
