Small pH Gradients Inhibit Cytochrome C Oxidase: Implications for H+ Entry to the Binuclear Center

doi:10.1006/bbrc.1995.2710

Biochemical and Biophysical Research Communications

Volume 216, Issue 3, 22 November 1995, Pages 931-938

https://doi.org/10.1006/bbrc.1995.2710 Get rights and content

Abstract

Respiring cytochrome c oxidase proteoliposomes generate internal alkalinity (ΔpH) and a membrane potential (ΔΨ). Valinomycin collapses ΔΨ, increases ΔpH, and slows steady state respiration. If ΔpH is heterogeneously expressed trapped probes will underestimate it. Internal pH changes were therefore followed in COV containing two buffer systems of differing pKs. The alkalinization rate at pH 7 was unaffected by adding AMPSO (pK 9.0) to the usual internal HEPES (pK 7.5). At higher pH, AMPSO slowed the approach to steady state. ΔpH inhibition is therefore not due to a large alkalinization in a small COV fraction. The O₂-reducing center may move protons via a local aqueous phase that is near electrical and pH equilibrium with the phase inside the COV. The dielectric in this membrane region can put the center electrically ′inside′ even though it is physically ′outside′.

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Cited by (6)

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In conclusion, the data presented here show that the pH inside the SUVs, i.e. the N-side, is alone responsible for the pH-dependence of the O2-reduction kinetics and fully determines the kinetics of both proton uptake and electron transfer in the studied pH-interval 6–9.5. These results are consistent with those obtained from earlier steady-state experiments with the mitochondrial enzyme [17]. In the light-driven proton pump bacteriorhodopsin the protonation state (determined by the pH) of a proton-release group influences the rate of proton release and order of specific reaction steps during the photocycle [26,27], which suggests that the pH on the proton-exit side may influence the proton-release rate.
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Regular ArticleSmall pH Gradients Inhibit Cytochrome C Oxidase: Implications for H+ Entry to the Binuclear Center

Abstract

Regular Article
Small pH Gradients Inhibit Cytochrome C Oxidase: Implications for H⁺ Entry to the Binuclear Center