Abstract
The vitamin B_6 requirement of Saccharomyces carlsbergensis 4228 (original and serine-adapted strain) in each thiamine added medium containing alanine, serine, phenylalanine or glutamic acid and methionine as the nitrogen source was investigated. The vitamin B_6 requirement in the alanine or serine medium was significantly higher than those in the phenylalanine or glutamate-methionine medium, in correspondance with strong inhibition or no inhibition of the growth by addition of thiamine. Each vitamin B_6 requirement of the yeast in simple nitrogen source was shown to be closely related with the maximal vitamin B_6 content of the yeast cells during the growth in the medium with thiamine. These findings suggest that the growth-inhibition of the yeast by thiamine was observed, when the vitamin B_6 content of the yeast is depressed below the level corresponding to the vitamin B_6 requirement through the inhibition of vitamin B_6 biosynthesis by thiamine in the yeast cells.
