title: Effects of cytochrome c on the oxidation of reduced cytochrome c oxidase by hydrogen peroxide.
abstract: The oxidation of the redox centres in reduced cytochrome c oxidase by hydrogen peroxide was studied by stopped-flow spectrophotometry in the absence and presence of reduced cytochrome c. The oxidation rate of cytochrome a decreased in the presence of cytochrome c. This effect was more pronounced at low than at high ionic strength. Cytochrome c did not influence the time-course of the oxidation of CuA or cytochrome a3. The oxidation of cytochrome c itself was faster at low ionic strength. The results suggest that the effect of cytochrome c is caused by re-reduction of cytochrome a by cytochrome c, the rate of which is dependent upon the ionic strength. We conclude that cytochrome a and cytochrome c are in equilibrium and that the equilibrium constant depends on the ionic strength. At low ionic strength, as a complex is formed between cytochrome c and cytochrome c oxidase, cytochrome a is more reduced than at high ionic strength conditions, when no such complex exists. Since CuA is oxidized at the same rate whether cytochrome c is present or not, we conclude that electron transfer from cytochrome a or cytochrome c to CuA is slower than electron transfer from CuA to cytochrome a or/and to the cytochrome a2-CuB couple.
authors.affiliation: E.C. Slater Institute, University of Amsterdam, The Netherlands.
authors.forename: A L
authors.initials: AL
authors.lastname: Lodder
authors.forename: R
authors.initials: R
authors.lastname: Wever
authors.forename: B F
authors.initials: BF
authors.lastname: van Gelder
mesh_terms: D003300:Copper; D003574:Cytochrome c Group / Q000737:chemistry*; D004579:Electron Transport; D003576:Electron Transport Complex IV / Q000737:chemistry*; D006861:Hydrogen Peroxide / Q000737:chemistry*; D010084:Oxidation-Reduction
chemical_list: D003574:Cytochrome c Group; D003300:Copper; D006861:Hydrogen Peroxide; D003576:Electron Transport Complex IV