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Exploring the proton pump mechanism of cytochrome c oxidase in real time.

ABSTRACT: Cytochrome c oxidase catalyzes most of the biological oxygen consumption on Earth, a process responsible for energy supply in aerobic organisms. This remarkable membrane-bound enzyme also converts free energy from O(2) reduction to an electrochemical proton gradient by functioning as a redox-linked proton pump. Although the structures of several oxidases are known, the molecular mechanism of redox-linked proton translocation has remained elusive. Here, correlated internal electron and proton transfer reactions were tracked in real time by spectroscopic and electrometric techniques after laser-activated electron injection into the oxidized enzyme. The observed kinetics establish the long-sought reaction sequence of the proton pump mechanism and describe some of its thermodynamic properties. The 10-micros electron transfer to heme a raises the pK(a) of a "pump site," which is loaded by a proton from the inside of the membrane in 150 micros. This loading increases the redox potentials of both hemes a and a(3), which allows electron equilibration between them at the same rate. Then, in 0.8 ms, another proton is transferred from the inside to the heme a(3)/Cu(B) center, and the electron is transferred to Cu(B). Finally, in 2.6 ms, the preloaded proton is released from the pump site to the opposite side of the membrane.

SUBMITTER: Belevich I

PROVIDER: S-EPMC1796784 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Initiation of the proton pump of cytochrome c oxidase.

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Multiscale simulations reveal key features of the proton-pumping mechanism in cytochrome c oxidase.

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Redox-dependent conformational changes in cytochrome C oxidase suggest a gating mechanism for proton uptake.

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