Abstract
Equilibration of the butyltriphenyl phosphonium (BTPP +) cation into cytochrome c oxidase reconstituted proteoliposomes was measured potentiometrically. The maximum membrane potential (Δψ) 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 Δψ 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. Δψ 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 Δψ. The value of Δψ 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.
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