Cytochrome oxidase: pathways for electron tunneling and proton transfer |
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Authors: | Bo G. Malmström |
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Affiliation: | (1) Department of Chemistry, Biochemistry and Biophysics, Gothenburg University, P.O. Box 462, SE-405 30 Gothenburg, Sweden, SE |
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Abstract: | Electrons from cytochrome c, the substrate of cytochrome oxidase, a redox-linked proton pump, are accepted by CuA in subunit II. From there they are transferred to the proton pumping machinery in subunit I, cytochrome a and cytochrome a 3–CuB. The reduction of the latter site, which is the dioxygen reducing unit, is coupled to proton uptake. Dioxygen reduction involves a peroxide and a ferryl ion intermediate, and it is the transition between these and back to the resting oxidized enzyme that are coupled to proton pumping. The X-ray structures suggest electron–transfer pathways that can account for the observed rates provided that the reorganization energies are small. They also reveal two proton-transfer pathways, and mutagenesis experiments have shown that one is used for proton uptake during the initial reduction of cytochrome a 3–CuB, whereas the other mediates transfer of the pumped protons. Received: 23 March 1998 / Accepted: 11 May 1998 |
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Keywords: | Cytochrome c Cytochrome oxidase Electron transfer Dioxygen reduction Proton pump |
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