Saccharomyces cerevisiae does not accumulate ethanol against a concentration gradient

Abstract

Accumulation does not occur and ethanol permeates the yeast cell plasma membrane by simple diffusion. Uptake and outflow of ethanol in yeast cells followed 1st-order kinetics and were insensitive to the presence of structural analogs of ethanol, to drastic pH changes, and to the action of reagents of amino and thiol groups. Ethanol apparently permeates the yeast cell plasma membrane without involvement of any carrier. The outflow rate of ethanol seems greater than the ability of this organism to produce ethanol, indicating that intracellulular accumulation of ethanol is not possible. The intracellular concentration of ethanol found was similar to the concentration in culture media in all tested conditions. The inadequacy of the cell-sampling procedure and of the chromatographic conditions used by other authors suggests that the discrepancy of results may be due to artifacts in the measurements of ethanol.