Kinetic mechanism of ATP synthesis catalyzed by mitochondrial F-0 center dot F-1-ATPase

Initial rates of succinate-dependent ATP synthesis catalyzed by submitochon drial particles from bovine heart substoichiometrically coupled with oligom ycin were found to have hyperbolic dependencies on contents of Mg ADP, free Mg2+, and phosphate. The results suggest that Mg.ADP complex and free phos phate are true substrates of the enzyme; and an unordered tertiary complex of F-0.F-1-ATPase, Mg.ADP, and phosphate is generated during the catalysis. The presence of free Mg2+ is required for the reaction. Mg2+ was a noncomp etitive activator of ATP synthesis relative to Mg.ADP and a competitive act ivator relative to phosphate. The decrease in steady-state values of Delta mu(H+) (by the inhibition of succinate oxidase with malonate) results in th e decreased value of V-max and in a slight decrease in K-m for the substrat es and Mg2+ without changes in affinity for the substrates. Based on these results, a kinetic scheme of ATP synthesis is proposed.