Peroxide-induced spectral perturbations of the 280-nm absorption band of cytochrome c oxidase.
It is now widely believed that the first two electrons transferred to the dioxygen reduction site in cytochrome c oxidase (CcO) are not coupled to proton translocation. The activation of the pump cycle correlates with the binding of dioxygen to the binuclear center. In order to investigate conformational changes in CcO associated with the formation of dioxygen intermediates during the catalytic cycle of CcO, the effects of hydrogen peroxide binding to CcO have been examined using UV optical absorption and second derivative techniques. Our data indicates that in the presence low concentrations of H2O2 (2:1 molar ratio) an initial CcO-peroxide species is formed in which the 280-nm absorption band is red shifted. This red shift occurs prior to spectral changes associated with H2O2 binding to cytochrome a3. Upon addition of higher concentrations of H2O2 (> 10 equivalents of H2O2 per equivalent of CcO) oxidized CcO is converted to F-state enzyme with no corresponding shift at 280 nm. It is suggested that H2O2 initially binds to CuB2+ resulting in a conformational change in the enzyme giving rise to a red-shifted 280 nm band. The absence of any conformational changes in F-state enzyme is consistent with the lack of bridging interactions with CuB2+ in this intermediate.
Larsen
R W
RW
Department of Chemistry, University of Hawaii at Manoa, Honolulu 96822.
D000818:Animals; D002417:Cattle; D003576:Electron Transport Complex IV / Q000737:chemistry* / Q000187:drug effects / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000378:metabolism / Q000494:pharmacology*; D010084:Oxidation-Reduction; D011485:Protein Binding; D011487:Protein Conformation / Q000187:drug effects; D013056:Spectrophotometry, Ultraviolet
D006861:Hydrogen Peroxide; D003576:Electron Transport Complex IV