title: Membrane-potential-dependent changes in the stoichiometry of charge translocation by the mitochondrial electron transport chain.
abstract: The charge/oxygen (q+/O) stoichiometry of mitochondria respiring on succinate was measured under conditions of high membrane potential (delta psi). The technique used was a variation of the steady-state method of Al-Shawi and Brand [(1981) Biochem. J. 200, 539-546]. We show that q+/O was about 2.7 at high values of delta psi (170 mV). As delta psi was lowered from 170 mV to 85 mV with the respiratory inhibitor malonate the q+/O stoichiometry increased to 6.0. A number of artefacts which could have led to an underestimation of the q+/O stoichiometry were eliminated. These included effects of any rapid change in mitochondrial volume, internal pH, activity of the endogenous K+/H+ exchanger or in H+ conductance due to changes in delta psi after the addition of inhibitor. The experiments presented here are the first direct demonstration that the stoichiometry of proton pumping by the mitochondrial respiratory chain changes as delta psi is varied.
authors.affiliation: Department of Biochemistry, University of Cambridge, England.
authors.forename: M P
authors.initials: MP
authors.lastname: Murphy
authors.forename: M D
authors.initials: MD
authors.lastname: Brand
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D004553:Electric Conductivity; D004579:Electron Transport; D006863:Hydrogen-Ion Concentration; D008314:Malonates / Q000494:pharmacology; D008564:Membrane Potentials; D008689:Methacrylates; D008930:Mitochondria, Liver / Q000032:analysis / Q000187:drug effects / Q000378:metabolism*; D008933:Mitochondrial Swelling / Q000187:drug effects; D010101:Oxygen Consumption / Q000187:drug effects; D011522:Protons; D051381:Rats; D013386:Succinates / Q000378:metabolism; D019802:Succinic Acid; D013844:Thiazoles / Q000494:pharmacology
chemical_list: D008314:Malonates; D008689:Methacrylates; D011522:Protons; D013386:Succinates; D013844:Thiazoles; C030517:myxothiazol; C030290:malonic acid; D019802:Succinic Acid