EFFECT OF HYDROGEN-PEROXIDE ON SUGAR-TRANSPORT IN SCHIZOSACCHAROMYCES-POMBE - ABSENCE OF MEMBRANE LIPID-PEROXIDATION

Stationary unaerated cells of S. pombe containing endogenous substrate s but not energized by any exogenous ones take up 2-deoxy-glucose, 6-d eoxy-D-glucose, D-xylose and D-arabinose actively over diffusion equil ibrium. The active uptake is inhibited by 20- 100 mmol/L H2O2 which ca uses an increase in K(T) but has no effect on J(max). This ''competiti ve inhibition'' indicates that H2O2 affects directly the sugar binding sites of the transporters. The ATP-binding site of the plasma membran e H+-ATPase is also affected by 100 mmol/L H2O2; the K(T) decreases 7- fold, J(max) about 2.5-fold. These effects are not likely to be mediat ed by membrane lipid peroxidation which appears to be lacking in S. po mbe, and this lack may be one of the reasons for the high resistance o f this yeast to H2O2. Because of this S. pombe represents a suitable s ystem for studying direct effects of oxidants on membrane proteins.