Effect of pH on the synthesis of cell carbohydrate during fermentation by baker's yeast

Abstract

1. 1. In the complete fermentation of 2 mg of glucose by 10 mg of a baker's yeast the fermentation rate and percentage conversion of glucose to cell carbohydrate were unaltered when the pH of the external medium was changed from 4.5 to 7.0. 2. 2. At pH 8.5 the fermentation rate was inhibited to 50% of the value at pH 4.5 or 7.0, but the percentage carbohydrate synthesis was unaltered. The finding of Sussman et al. 1, that raising the pH of the fermentation medium resulted in decreased cellular carbohydrate synthesis, is therefore not of general application. 3. 3. It is pointed out that the percentage conversion to carbohydrate depends on at least five factors, all of which may be altered by changes of internal pH induced by change in the pH of the medium. The discussion of Sussman et al., postulating a direct effect of external pH on the equilibrium constant of the yeast phosphorylase, appears to be an over-simplification of the picture.