Steady-state coupling of four membrane systems in mitochondrial oxidative phosphorylation.

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Abstract
According to Alexandre, Reynafarje and Lehninger, 4 different membrane systems are involved, with definite stoichiometry, in the mitochondrial synthesis of ATP by electron transport, via proton transport. Some thermodynamic consequences of this model are discussed. At steady state, each of the 4 systems must have the same flux J through the membrane. The overall thermodynamic force X for oxidative phosphorylation is the sum of the 4 separate forces. From these properties, using an empirical linear flux-force relation for each system, J can be obtained as a function of X. X depends on the inside [NAD+]/[NADH] and the outside [ATP]/[ADP][Pi] quotients (and on the pH inside). J is related to these quotients; the relationship derived is similar to that described by Erecinska and Wilson, as deduced from a quite different model of oxidative phosphorylation. Proton transport is involved explicitly in 3 of the 4 systems of the present model. Because of the steady-state stoichiometric coupling of the 4 systems, proton transport does not appear in the overall reaction. Erecinska and Wilson used, in their model, a direct connection between electron transport and ATP synthesis. J can be related to the quotients without this direct connection.