ETHANOL TOLERANCE AND ACTIVITY OF PLASMA-MEMBRANE ATPASE IN KLUYVEROMYCES-MARXIANUS AND SACCHAROMYCES-CEREVISIAE

The activity of plasma membrane ATPase was compared in cells of differently ethanol-tolerant strains of Kluyveromyces marxianus and Saccharomyces cerevisiae grown with increasing concentrations of ethanol. Depending on the concentration, ethanol activated or inhibited this membrane enzyme, and the percentage of inhibition per unit of ethanol was higher for the low-ethanol tolerant K. marxianus IGC 2671. Only for ethanol concentrations near the maximal for growth [range 5-7% (v/v) for K. marxianus and 8-10% (v/v) for S. cerevisiae], the ATPase activity reached values below those in cells grown in the absence of added ethanol. Plasma membrane ATPase activity was approximately 200 nmol P(i) min-1 mg-1 in cells of both strains grown with the maximal concentration of ethanol that allowed balanced growth [7% or 10% (v/v)]. This value was about 23% of the maximal level attained (900 nmol P(i) min-1 mg-1 for both strains) when plasma membrane ATPase was fully activated by ethanol [3% or 6% (v/v), respectively for the low- or the high-ethanol tolerant strain]. A correlation was established between plasma membrane ATPase activity in cells grown with ethanol and their ethanol tolerance using as a criterion its inhibitory effects on growth.