Time-resolved optical absorption studies of cytochrome oxidase dynamics

• Published in: BBA - Bioenergetics Vol. 1655; no. 1-3; pp. 263 - 273
• Main Authors: Einarsdóttir, Ólöf, Szundi, Istvan
• Format: Book Review Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 12-04-2004
• Subjects: Animals; Branched mechanism; Cattle; Electron Spin Resonance Spectroscopy; Electron Transport; Electron Transport Complex IV - chemistry; Electron Transport Complex IV - metabolism; Flow-flash; Hydrogen-Ion Concentration; In Vitro Techniques; Models, Chemical; Myocardium - enzymology; Oxidation-Reduction; Oxygen - metabolism; Oxygen carrier; Photolysis; Proton-Motive Force; Spectrophotometry; Spectroscopy, Fourier Transform Infrared; Tyrosine - chemistry; Tyrosyl radical; Water - metabolism; Oxygen carrier; Flow-flash; Tyrosyl radical; Branched mechanism
• ISSN: 0005-2728; 0006-3002; 1879-2650
• DOI: 10.1016/j.bbabio.2003.07.011

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.