The reaction of the electrostatic cytochrome c-cytochrome oxidase complex with oxygen.
The reaction of the electrostatic cytochrome c-cytochrome oxidase complex with oxygen is measured by transient absorption spectroscopy. The oxygen reaction is initiated by photolytic removal of CO from cytochrome oxidase, using a flash-pumped dye laser. The subsequent reaction of the cytochrome c-cytochrome oxidase complex with oxygen is reported at 550, 605, 744, and 830 nm at different cytochrome c:cytochrome oxidase ratios and different oxygen concentrations. In the absence of cytochrome c the time course of the reaction of the oxidase is well described by a triple exponential process at any of the measured wavelengths. The three processes are well resolved at high O2 levels (i.e. greater than 200 microM), where they reach first-order rate limits of 2.4 x 10(4), 7.5 x 10(3), and 650 s-1. When cytochrome c is added the oxidation of cytochrome a and one of the redox active cooper centers (CuA) are interrupted. The maximal effect of cytochrome c on the oxidation of the oxidase occurs at a c:aa3 ratio of 1. Cytochrome c reacts in a biphasic process with rates of up to 7 x 10(3) and 550 s-1 at high oxygen. The fast phase takes up 60% of the process, and this is independent of the cytochrome c:cytochrome oxidase ratio. The results are discussed in the context of a model in which electron entry into cytochrome oxidase from cytochrome c is via CuA, and cytochrome a functions to mediate electron transfer from CuA to the oxygen binding site. The role of CuA as initial electron acceptor in cytochrome c oxidase is related to its physical proximity to cytochrome c is the cytochrome c-cytochrome oxidase complex.
Hill
B C
BC
Department of Chemistry and Biochemistry, Concordia University, Montreal, Quebec, Canada.
D000818:Animals; D002417:Cattle; D003300:Copper / Q000378:metabolism; D003574:Cytochrome c Group / Q000378:metabolism*; D004579:Electron Transport; D003576:Electron Transport Complex IV / Q000378:metabolism*; D006736:Horses; D007700:Kinetics; D009994:Osmolar Concentration; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism*; D013057:Spectrum Analysis
D003574:Cytochrome c Group; D003300:Copper; D003576:Electron Transport Complex IV; D010100:Oxygen