title: Electron transfer between cytochrome a and copper A in cytochrome c oxidase: a perturbed equilibrium study.
abstract: Intramolecular electron transfer in partially reduced cytochrome c oxidase has been studied by the perturbed equilibrium method. We have prepared a three-electron-reduced, CO-inhibited form of the enzyme in which cytochrome a and copper A are partially reduced and in an intramolecular redox equilibrium. When these samples were irradiated with a nitrogen laser (0.6-ns, 1.0-mJ pulses) to photodissociate the bound CO, changes in absorbance at 598 and 830 nm were observed which were consistent with a fast electron transfer from cytochrome a to copper A. The absorbance changes at 598 nm gave an apparent rate of 17,000 +/- 2000 s-1 (1 sigma), at pH 7.0 and 25.5 degrees C. These changes were not observed in either the CO mixed-valence or the CO-inhibited fully reduced forms of the enzyme. The rate was fastest at about pH 8.0, falling off toward both lower and higher pHs. There was a small but clear temperature dependence. The process was also observed in the cytochrome c-cytochrome c oxidase high-affinity complex. The electron equilibration measured between cytochrome a and copper A is far faster than any rate measured or inferred previously for this process.
authors.affiliation: Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena 91125.
authors.forename: J E
authors.initials: JE
authors.lastname: Morgan
authors.forename: P M
authors.initials: PM
authors.lastname: Li
authors.forename: D J
authors.initials: DJ
authors.lastname: Jang
authors.forename: M A
authors.initials: MA
authors.lastname: el-Sayed
authors.forename: S I
authors.initials: SI
authors.lastname: Chan
mesh_terms: D000818:Animals; D003300:Copper / Q000378:metabolism*; D017936:Cytochrome a Group; D003580:Cytochromes / Q000378:metabolism*; D004579:Electron Transport; D003576:Electron Transport Complex IV / Q000378:metabolism*; D006736:Horses; D007700:Kinetics; D008929:Mitochondria, Heart / Q000378:metabolism; D010084:Oxidation-Reduction; D013053:Spectrophotometry; D013997:Time Factors
chemical_list: D017936:Cytochrome a Group; D003580:Cytochromes; D003300:Copper; D003576:Electron Transport Complex IV