Inhibition of Yeast Growth by Methionine

Part III. Methionine as an Inhibitor of Conversion from Fermentative to Respiratory Processes

Abstract

Growth of a baker's yeast was inhibited at definite cell concentrations when cells were incubated in a glucose medium containing L-methionine under semi-aerobic conditions. A little or no significant growth inhibition by methionine was observed when the cells were cultured under very aerobic or anaerobic conditions. Under semi-aerobic conditions glucose was first metabolized by the fermentative process yielding almost theoretical amounts of ethanol. The secondary growth occurred at the expense of accumulated ethanol by oxidative metabolism. Methionine inhibited the utilization of ethanol as well as the secondary growth without affecting glucose fermentation and the primary growth. Manometric experiments revealed that cells grown in the absence of methionine showed vigorous respiratory activities towards ethanol substrate. This oxidation was not affected by the addition of methionine. On the contrary, cells grown in the presence of methionine exhibited only feeble oxidative activities with ethanol. Therefore, methionine inhibits the formation of respiratory enzymes responsible for the oxidation of ethanol. The possible mechanism of this inhibition was discussed.