Studies on stabilization of the oxidative phosphorylation system. 3. The effects of substrates and ATP on sensitivity of various energy-linked functions of submitochondrial particles to phospholipase a from Crotalus terrificus venom.

Abstract

The following results have been obtained from the study of the action of phospholipase A fromCrotalus terrificus venom on sonic submitochondrial particles: (1) The rate of ATP-dependent NAD+ reduction by succinate and the rates of ATP- and succinate-dependent transhydrogenase reactions (NADH→NADP+) rapidly decreases on treatment of submitochondrial particles with phospholipase A. The rate of the ATP-Pi exchange reaction does not thereby significantly decrease. NADH: fumarate oxidoreductase and energy-independent trashydrogenase (NADH→NADP+) activities of the particles do not display a high sensitivity to phospholipase A either. (2) When the particles subjected to the action of phospholipase A carry out NADH oxidation or ATP hydrolysis, some energy-dependent functions are disturbed less readily. This refers to reversed electron transfer, the ATP-dependent transhydrogenase reaction and partially to the succiante-dependent transhydrogenase reaction. The protective effect is sensitive to uncouplers. The ability to catalyze the ATP-Pi exchange reaction is not preserved in these conditions. (3) These results suggest that coupling sites I and IV of sonic (“inside out”) submitochondrial particles are highly sensitive to phospholipase A fromCrotalus terrificus venom.