ETHANOL TOLERANCE AND ACTIVITY OF PLASMA-MEMBRANE ATPASE IN PICHIA-STIPITIS GROWN ON D-XYLOSE OR ON D-GLUCOSE

The use of glucose as the carbon source during the growth of Pichia st ipitis NRRL Y7124 increased the specific activity of the plasma membra ne ATPase three-fold in comparison to the activity measured with xylos e as the carbon source. Compared to the nonactivated enzyme, the gluco se-activated ATPase had the same pH and temperature optima, a comparab le affinity for ATP, a greater sensitivity to orthovanadate, and a low er sensitivity to ethanol. Furthermore, the ethanol concentration resu lting in growth inhibition depended on the nature of the sugar consume d: 30 or 34 g l(-1), respectively, when culture was grown on xylose or glucose. These results showed a correlation between plasma membrane A TPase activity in cells grown either on D-glucose or on D-xylose, and their ethanol tolerance, evaluated by the inhibitory effect of ethanol on growth. Finally, these data, added to the in vitro effect of ethan ol on the plasma membrane ATPase, suggested that a decrease of ATPase activity to <60% of the control (measured without alcohol in the test) would prevent the growth of P. stipitis.