Kinetics of ATP Synthesis in Pea Cotyledon Submitochondrial Particles

A kinetic study of oxidative phosphorylation by pea submitochondrial particles gave two K(m) values for ADP, one low, the other high. The high value probably reflected a damaged site or a population of leaky mitochondria. Only the high affinity site with a low K(m) for ADP was involved in ATP synthesis. alpha,beta-Methylene ADP was found to be a competitive inhibitor of ATP synthesis. The inorganic phosphate analog, thiophosphate, decreased the apparent K(m) of ADP while the rate of the reaction remained approximately the same. Adenyl imidodiphosphate, a specific inhibitor of ATP hydrolysis activity, had little effect on oxidative phosphorylation. A slight decrease in the K(m) of the high affinity binding site for ADP was noted. Aurovertin was found to be a potent inhibitor of oxidative phosphorylation in pea submitochondrial particles. The K(m) of the high affinity site was increased 10-fold. Also, the inhibition normally exerted by ADP on ATPase activity was severely reduced by aurovertin. In contrast, increasing the concentration of aurovertin only slightly affected the level of inhibition caused by adenyl imidodiphosphate on ATP hydrolysis.