Control of transmembrane charge transfer in cytochrome c oxidase by the membrane potential

Abstract

The respiratory chain in mitochondria is composed of membrane-bound proteins that couple electron transfer to proton translocation across the inner membrane. These charge-transfer reactions are regulated by the proton electrochemical gradient that is generated and maintained by the transmembrane charge transfer. Here, we investigate this feedback mechanism in cytochrome c oxidase in intact inner mitochondrial membranes upon generation of an electrochemical potential by hydrolysis of ATP. The data indicate that a reaction step that involves proton uptake to the catalytic site and presumably proton translocation is impaired by the potential, but electron transfer is not affected. These results define the order of electron and proton-transfer reactions and suggest that the proton pump is regulated by the transmembrane electrochemical gradient through control of internal proton transfer rather than by control of electron transfer.

The Redox-Active Tyrosine Is Essential for Proton Pumping in Cytochrome c Oxidase

“…For example, in the F R state, the new electron is on the tyrosine and the high-spin heme is still in the Fe a 3 (IV) state, but when the proton has reached the BNC, forming the O H state, the high-spin heme turns into Fe a 3 (III). This scheme for reduction of the F state agrees with experimental observations ( Björck and Brzezinski, 2018 ).…”

Broadband fluorescence reveals mechanistic differences in excited-state proton transfer to protic and aprotic solvents

“…Acid-base reactions, such as proton dissociation, transport and neutralization, play a pivotal role in several chemical, biological as well as technological processes. [1][2][3][4][5][6][7][8][9] However, detailed investigation on the proton-transfer dynamics in solution is challenging due to the dynamic nature of the dissociationassociation equilibrium. Excited-state proton transfer (ESPT) to solvent serves as a model system for the ground-state reaction and therefore remains as an active topic in chemical sciences.…”

Beating Heart of Cytochrome c Oxidase: The Shared Proton of Heme a3 Propionates

“…Identifying the nature of the pump-active PLS experimentally may be very difficult, since the lifetime of the protonated PLS is likely very short and may be in the microsecond time regime. It is even more difficult since the time course of the reaction cycle cannot be controlled precisely . Studying the behavior of mutants may help, but bears the risk of uncontrolled structural changes, if not accompanied by crystallographic structure determination.…”

“…It is even more difficult since the time course of the reaction cycle cannot be controlled precisely. 53 Studying the behavior of mutants may help, but bears the risk of uncontrolled structural changes, if not accompanied by crystallographic structure determination. Time-resolved infrared spectroscopy in a stopped-flow apparatus 53 may help, if applied to isotopically labeled heme propionates.…”

“…53 Studying the behavior of mutants may help, but bears the risk of uncontrolled structural changes, if not accompanied by crystallographic structure determination. Time-resolved infrared spectroscopy in a stopped-flow apparatus 53 may help, if applied to isotopically labeled heme propionates. Replacing protons by deuterons may also help, since it slows down the processes and stabilizes the protonated state of the pumpactive PLS.…”