Thh kinetics and thermodynamics of ox1dative phosphorylation

The mitochondrial process of oxidative phosphorylation has usually been studied in I he presence of high concentrations of O₂ by determining the extent and rates of O₂ uptake and ATP synthesis. In this study, the time course of both O₂ consumption and ATP synthesis are simultaneously determined in reactions initiated by adding O, to anaerobic suspensions of mitochondria in which the back flow of H' is at a minimum and the flow of electrons is opposed by zero resistance in the forms of AGP and A [iH'. The following novel characteristics of oxidative phosphorylation are found. I. ACip is a direct function of O₂ concentration, regardless of protein and ADP concentration. 2. The reduction andor protonation of the entire membrane is crucial for the extremely rapid rates of ATP synthesis, 3. The initial steady-state rates of ATP synthesis are perfectly compatible with the very fast rates of O, consumption and net flow of electrons characteristic of the first phase of the respiratory process. 4. The initial rates of ATP synthesis, depend on the concentrations of either O₂ or ADP strictly in accordance with the Michaelis-Meuten rate equation, provided the other 4 substrates of oxidative phosphorylation (H', e', Pi, and either ADP or O,) are maintained in excess. It is concluded that all catalytic sites in the F, moiety of the ATP synthase are kinetically equivalent in synthesizing ATP.