Proton translocation by cytochrome c oxidase in different phases of the catalytic cycle.
Since mitochondrial cytochrome c oxidase was found to be a redox-linked proton pump, most enzymes of the haem-copper oxidase family have been shown to share this function. Here, the most recent knowledge of how the individual reactions of the enzyme's catalytic cycle are coupled to proton translocation is reviewed. Two protons each are pumped during the oxidative and reductive halves of the cycle, respectively. An apparent controversy that concerns proton translocation during the reductive half is resolved. If the oxidised enzyme is allowed to relax in the absence of reductant, the binuclear haem-copper centre attains a state that lies outside the main catalytic cycle. Reduction of this form of the enzyme is not linked to proton translocation, but is necessary for a return to the main cycle. This phenomenon might be related to the previously described "pulsed" vs. "resting" and "fast" vs."slow" forms of haem-copper oxidases.
Wikström
Mårten
M
Helsinki Bioenergetics Group, Institute of Biotechnology, Programme for Structural Biology and Biophysics, University of Helsinki, PB 65, FI-00014 Helsinki, Finland. marten.wikstrom@helsinki.fi
Verkhovsky
Michael I
MI
D002384:Catalysis; D004563:Electrochemistry; D003576:Electron Transport Complex IV / Q000737:chemistry*; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000737:chemistry; D017494:Proton Pumps / Q000737:chemistry*; D013816:Thermodynamics
D017494:Proton Pumps; D010088:Oxidoreductases; C024748:copper oxidase; D003576:Electron Transport Complex IV