DECREASE IN YEAST GLUCOSE-6-PHOSPHATE-DEHYDROGENASE ACTIVITY DUE TO OXYGEN-FREE RADICALS

1. u.v. radiations and copper acetate, as free radical generating syst ems, determine a significant diminishing of glucose-6-phosphate dehydr ogenase activity in the homogenates of Saccharomyces cerevisiae. 2. Th e inactivation is proportional to the concentration of the formed free radicals, existing a direct dependence on the action time of the free radicals generating systems and on the irradiation dose. The decrease of the enzyme catalytic activity is correlated with the increase of t he malondialdehyde concentration. 3. The affinity for the substrate of the enzyme under the action of free radicals does not change signific antly compared to the native enzyme: the K-m value for NADP is halved, whilst that for glucose-6-phosphate remains unchanged. 4. The electro phoretic study shows evidence of five electrophoretic bands with enzym atic activity in the native extract and the disappearance of one molec ular form under the free radical action.