Effect of Thiamine on Ethanol and Pyruvate Production in Helminthosporium maydis

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Abstract
Growth of the fungus Helminthosporium maydis race T in a basal glucose-L-asparagine liquid medium, pH 5, was inhibited by thiamine-HCl. Analysis of the media for organic acids revealed that the extracellular pyruvate concentration decreased as the thiamine-HCl concentration of the medium increased. Extracellular ethanol, in contrast to pyruvate, increased in concentration as the thiamine-HCl concentration of the medium increased under both aerobic and anaerobic conditions. The changes in ethanol and pyruvate levels in the presence of thiamine-HCl occurred via a thiamine-mediated increase in the activity of pyruvate decarboxylase but not alcohol dehydrogenase. This increase in pyruvate decarboxylase activity appeared to be due to an increase in the quantity of enzyme present rather than an activation of pre-existing enzyme. Whereas thiamine-pyrophosphate stimulated pyruvate decarboxylase activity in vitro, thiamine-HCl had no effect. Neither thiamine derivative affected alcohol dehydrogenase activity. The increase in pyruvate decarboxylase activity which accompanied an increase in the thiamine-HCl concentration of the medium was correlated with a decrease in the level of intracellular pyruvate.