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Kinetics of ATP Synthesis in Pea Cotyledon Submitochondrial Particles ¹

Department of Plant Science, University of Alberta, Edmonton, Alberta, Canada, T6G 2H1

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. ,-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.

³ To whom reprint requests should be addressed.

¹ We gratefully acknowledge the assistance of the Natural Sciences and Engineering Research Council of Canada in the form of a grant (A-1451) to M. S. in aid of this research and a Postdoctoral Fellowship for D. L. M.

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