Upper and lower limits of the charge translocation stoichiometry of mitochondrial electron transport

Abstract

The upper and lower limits of the mechanistic stoichiometry (n) of electric charge translocation coupled to mitochondrial electron transport have been determined for the oxidation of succinate and beta-hydroxybutyrate using a recently described method (Beavis, A. D., and Lehninger, A. L. (1986) Eur. J. Biochem. 158, 307-314). This method requires no assumptions regarding the magnitude of proton leakage or pump slippage, but it takes advantage of the ability to predict the direction of change as the coupled fluxes are modulated by specific means. In this study, the rates of K+ uptake (JK) and O2 consumption (JO) were determined from simultaneous electrode measurements in the presence of various concentrations of valinomycin or inhibitors of electron flow. When valinomycin is varied, the rate of proton leakage or pump slippage should decrease as JO increases, with the result that the slope dJK/dJO will be greater than n. On the other hand, when an inhibitor of electron flow is varied, the rate of proton leakage or pump slippage should increase as JO increases, with the result that the slope dJK/dJO should be less than n. The data obtained using this approach indicate that n lies between 6.7 and 7.3 for succinate oxidation and between 10.2 and 11.7 for beta-hydroxybutyrate (or NADH) oxidation. It is concluded that the mechanistic stoichiometry of charge separation coupled to electron flow is 7 q+/O in the span from succinate to oxygen and 11 q+/O in the span from NADH to oxygen. These conclusions are fully consistent with the limits of the mechanistic ATP/O ratios previously determined for these spans (Beavis, A. D., and Lehninger, A. L. (1986) Eur. J. Biochem. 158, 315-322).