Kinetic Mechanism of ATP Synthesis Catalyzed by Mitochondrial F_o·F₁-ATPase

M. A. Galkin^* and A. V. Syroeshkin

Department of Biochemistry, School of Biology, Lomonosov Moscow State University, Moscow, 119899 Russia; fax: (095) 939-3955; E-mail: adv@biochem.bio.msu.su

^* To whom correspondence should be addressed.

Received March 22, 1999; Revision received April 27, 1999

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Initial rates of succinate-dependent ATP synthesis catalyzed by submitochondrial particles from bovine heart substoichiometrically coupled with oligomycin were found to have hyperbolic dependencies on contents of Mg·ADP, free Mg²⁺, and phosphate. The results suggest that Mg·ADP complex and free phosphate are true substrates of the enzyme; and an unordered ternary complex of F_o·F₁-ATPase, Mg·ADP, and phosphate is generated during the catalysis. The presence of free Mg²⁺ is required for the reaction. Mg²⁺ was a noncompetitive activator of ATP synthesis relative to Mg·ADP and a competitive activator relative to phosphate. The decrease in steady-state values of Deltaµ_H+ (by the inhibition of succinate oxidase with malonate) results in the decreased value of V_max and in a slight decrease in K_m for the substrates and Mg²⁺ without changes in affinity for the substrates. Based on these results, a kinetic scheme of ATP synthesis is proposed.

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KEY WORDS: F_o·F₁-ATPase, mitochondrion, Deltaµ_H+-dependent ATP synthesis

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