Effect of ethanol on cell growth, metabolism and cation fluxes in the yeast Metschnikowia reukaufii

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Abstract
The yeast Metschnikowia reukaufii could not utilize ethanol as a growth substrate, although ethanol stimulated cellular O2 consumption and the reduction of intracellular nicotinamide adenine nucleotides. Also, ethanol inhibited cell growth in glucose-containing medium. The effect was stronger when the K+ concentration in the growth medium was lowered from 5.8 to 0.6 mM. Addition of glucose to an aerated cell suspension caused an initial H+ efflux and K+ influx in a ratio of approximately 1:1. This was followed by a phase of continuing extracellular acidification without any measurable uptake of K+. In contrast, in cells energized by glucose, ethanol stimulated K+ efflux; concomitantly, H+ extrusion was markedly lowered by ethanol. The rates of H+ extrusion correlated with the intracellular level of glucose 6-phosphate and not of ATP. It is concluded that there is a regulatory interaction, though not by a direct effect, between glucose 6-phosphate and the plasma-membrane ATPase. Ethanol appears to activate electron transfer from cytosolic NADH to O2 by a pathway independent of the mitochondrial respiratory chain.