title: Time-resolved optical absorption studies of cytochrome oxidase dynamics.
abstract: Time-resolved spectroscopic studies in our laboratory of bovine heart cytochrome c oxidase dynamics are summarized. Intramolecular electron transfer was investigated upon photolysis of CO from the mixed-valence enzyme, by pulse radiolysis, and upon light-induced electron injection into the cytochrome c/cytochrome oxidase complex from a novel photoactivatable dye. The reduction of dioxygen to water was monitored by a gated multichannel analyzer using the CO flow-flash method or a synthetic caged dioxygen carrier. The pH dependence of the intermediate spectra suggests a mechanism of dioxygen reduction more complex than the conventional unidirectional sequential scheme. A branched model is proposed, in which one branch produces the P form and the other branch the F form. The rate of exchange between the two branches is pH-dependent. A cross-linked histidine-phenol was synthesized and characterized to explore the role of the cross-linked His-Tyr cofactor in the function of the enzyme. Time-resolved optical absorption spectra, EPR and FTIR spectra of the compound generated after UV photolysis indicated the presence of a radical residing primarily on the phenoxyl ring. The relevance of these results to cytochrome oxidase function is discussed.
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Santa Cruz, CA 95064, USA. olof@chemistry.ucsc.edu
authors.forename: Olöf
authors.initials: O
authors.lastname: Einarsdóttir
authors.forename: Istvan
authors.initials: I
authors.lastname: Szundi
mesh_terms: D000818:Animals; D002417:Cattle; D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport; D003576:Electron Transport Complex IV / Q000737:chemistry* / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008956:Models, Chemical; D009206:Myocardium / Q000201:enzymology; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D010782:Photolysis; D018892:Proton-Motive Force; D013053:Spectrophotometry; D017550:Spectroscopy, Fourier Transform Infrared; D014443:Tyrosine / Q000737:chemistry; D014867:Water / Q000378:metabolism
chemical_list: D014867:Water; D014443:Tyrosine; D003576:Electron Transport Complex IV; D010100:Oxygen