title: Membrane potentials in reconstituted cytochrome c oxidase proteoliposomes determined by butyltriphenyl phosphonium cation distribution.
abstract: Equilibration of the butyltriphenyl phosphonium (BTPP+) cation into cytochrome c oxidase reconstituted proteoliposomes was measured potentiometrically. The maximum membrane potential (delta psi) generated by oxidase activity was estimated to lie between -65 and -90 mV, vesicle interior negative, when internal BTPP+ binding is taken into account. Formation of delta psi was completely prevented by valinomycin and carbonyl-cyanide-p-trifluoromethoxyphenylhydrazone but only 10% inhibited by levels of N',N'-dicyclohexylcarbodiimide that abolish proton pumping by the oxidase. delta psi is thus maintained by at least one charge transfer process that does not involve proton movement. A nonlinear relationship was obtained between oxidase activity and steady-state delta psi. The value of delta psi estimated by BTPP+ distribution was lower than that calculated using the optical probes safranine and a carbocyanine dye. Possible reasons for this discrepancy are discussed.
mesh_terms: D000818:Animals; D001386:Azides / Q000494:pharmacology; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D002417:Cattle; D004024:Dicyclohexylcarbodiimide / Q000494:pharmacology; D004566:Electrodes; D003576:Electron Transport Complex IV / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000502:physiology; D004734:Energy Metabolism; D008081:Liposomes / Q000378:metabolism*; D008564:Membrane Potentials; D009550:Nigericin / Q000494:pharmacology; D009861:Onium Compounds; D009943:Organophosphorus Compounds; D019810:Sodium Azide; D014634:Valinomycin / Q000494:pharmacology
chemical_list: D001386:Azides; D008081:Liposomes; D009861:Onium Compounds; D009943:Organophosphorus Compounds; D014634:Valinomycin; C032536:butyltriphenylphosphonium; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D004024:Dicyclohexylcarbodiimide; D019810:Sodium Azide; D003576:Electron Transport Complex IV; D009550:Nigericin