EXPERIMENTAL DISCRIMINATION BETWEEN PROTON LEAK AND REDOX SLIP DURINGMITOCHONDRIAL ELECTRON-TRANSPORT

By measuring the relationship between protonmotive force and the incre ment in oxygen consumption by mitochondria treated with submaximal amo unts of uncoupler, we have experimentally tested four different models of imperfect coupling of oxidative phosphorylation. The results show that the increased rate of oxygen consumption at high protonmotive for ce is explained entirely by the dependence on protonmotive force of th e passive proton leak conductance of the mitochondrial inner membrane. There is no measurable contribution from redox-slip reactions in the proton pumps caused by high protonmotive force. Neither is there any c ontribution from increased proton conductance of the membrane or incre ased redox slip in the respiratory chain caused by high turnover rates of the complexes.