Current-voltage relationships for proton flow through the F0 sector of the ATP-synthase carbonylcyanide-p-trifluoromethoxyphenylhydrazone or leak pathways in submitochondrial particles

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Abstract
1. Respiring submitochondrial particles from which the F1 sector of ATP-synthase was displaced generated a membrane potential in the range of 115-140 mV. Addition of oligomycin raised the membrane potential by approximately 40 mV. The lower membrane potential in particles with F1 displaced is attributed to partial dissipation of the proton electrochemical gradient as a consequence of proton flow through the open proton channels provided by the Fo sectors of the ATP-synthase. 2. The characteristics of proton flow through the open Fo channels were studied by varying the rate of electron transport-driven proton translocation which permitted the establishement of a range of steady-state membrane potentials. Open Fo channels appeared to have a gated response to the membrane potential such that they were inoperative when the potential fell below approximately 110 mV. 3. The membrane potential was measured as a function of respiratory rate in intact Mg-ATP submitochondrial particles that had been treated with low concentrations of the protonophore carbonylcyanide-p-trifluoromethoxyphenylhydrazone. In general a linear dependence of membrane potential upon respiraotry rate was observed except at the lowest concentrations of protonophore and highest respiratory rates, presumably because the effect of the protonophore was then offset by an increased rate of proton translocation driven by the respiratory chain. 4. The effect of increasing concentrations of carbonycanide-p-trifluoromethoxyphenylhydrazone on the membrane potential of respiring submitochondrial particles was studied. It was found that equal amounts of the protonophore lowered the membrane potential to a lesser extent at lower values of the membrane potential. 5. Treatment of Mg-ATP submitochondrial particles with oligomycin slightly increased (by approximately 10 mV) the size of the respiration-dependent membrane potential, but did not alter the profile of membrane potential as a function of succinate oxidation rate. The latter was controlled by titration with malonate. This result indicates that the Fo sector of the ATP-synthase does not significantly contribute to leak pathways in intact submitochondrial particles.