title: Redox equilibration after one-electron reduction of cytochrome c oxidase: radical formation and a possible hydrogen relay mechanism.
abstract: Kinetic studies using UV/visible and EPR spectroscopy were carried out to follow the distribution of electrons within beef heart cytochrome c oxidase (CcO), both active and cyanide-inhibited, following addition of reduced cytochrome c as electron donor. In the initial one-electron reduced state the electron is shared between three redox centers, heme a, CuA and a third site, probably CuB. Using a rapid freeze system and the spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO) a protein radical was also detected. The EPR spectrum of the DMPO adduct of this radical was consistent with tyrosyl radical capture. This may be a feature of a charge relay mechanism involved in some part of the CcO electron transfer system from bound cytochrome c via CuA and heme a to the a3CuB binuclear center.
authors.affiliation: Biochemistry Unit, Department of Pre-Clinical Sciences, Faculty of Medical Sciences, University of the West Indies, St. Augustine, Trinidad and Tobago.
authors.forename: Damian
authors.initials: D
authors.lastname: Ashe
authors.affiliation: Biochemistry Unit, Department of Pre-Clinical Sciences, Faculty of Medical Sciences, University of the West Indies, St. Augustine, Trinidad and Tobago.
authors.forename: Trevor
authors.initials: T
authors.lastname: Alleyne
authors.affiliation: Molecular Biophysics Research Group, School of Biological Sciences, University of Essex, Colchester, Essex CO4 3SQ, UK.
authors.forename: Michael
authors.initials: M
authors.lastname: Wilson
authors.affiliation: Molecular Biophysics Research Group, School of Biological Sciences, University of Essex, Colchester, Essex CO4 3SQ, UK.
authors.forename: Dimitri
authors.initials: D
authors.lastname: Svistunenko
authors.affiliation: Molecular Biophysics Research Group, School of Biological Sciences, University of Essex, Colchester, Essex CO4 3SQ, UK. Electronic address: pnicholl@essex.ac.uk.
authors.forename: Peter
authors.initials: P
authors.lastname: Nicholls
mesh_terms: D000818:Animals; D002417:Cattle; D003497:Cyclic N-Oxides; D045304:Cytochromes c / Q000737:chemistry / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport; D003576:Electron Transport Complex IV / Q000737:chemistry* / Q000378:metabolism*; D005609:Free Radicals / Q000737:chemistry / Q000378:metabolism; D006736:Horses; D006859:Hydrogen / Q000378:metabolism; D007700:Kinetics; D008954:Models, Biological; D009206:Myocardium / Q000201:enzymology; D010084:Oxidation-Reduction; D013053:Spectrophotometry; D013113:Spin Labels
chemical_list: D003497:Cyclic N-Oxides; D005609:Free Radicals; D013113:Spin Labels; C017245:5,5-dimethyl-1-pyrroline-1-oxide; D006859:Hydrogen; D045304:Cytochromes c; D003576:Electron Transport Complex IV
keywords: Amino acid radical; Cyanide; Cytochrome c oxidase; DMPO; Electron transfer; Spin trap; Tryptophan; Tyrosine