Studies on yeast metabolism. 4. The effect of thiamine on yeast fermentation

Abstract

Thiamine, added to fermenting baker s yeast, lowers the intracellular pyruvate corresponding to a given fermentation rate. Kinetic studies suggest that this is caused, not by increased affinity of carboxylase for its substrate, but by the production of more enzyme. The rapidity of action is interpreted as showing that, at least in the early stages, actual protein synthesis is not involved, i.e. that the process is one of supplying coenzyme to pre-existing apocarboxylase. The pyruvate-lowering action of thiamine increases when 0.01-0.10 [mu] mole/g yeast is added, but the fermentation rate does not parallel thiamine increase above 0.01 [mu] mole/g. It is pointed out that effects on CO2 rate may depend upon the enzymic constitution of the particular yeast used. The pyruvate-lowering action of 2-methyl-4-amino-5-ethoxymethylpyrimi-dine is explained as due to the synthesis from it of 3 x 10-4 [mu]mole thiamine/minute/g yeast.