title: Identification of a ferryl intermediate of Escherichia coli cytochrome d terminal oxidase by resonance Raman spectroscopy.
abstract: The 680-nm-absorbing "peroxide state" of the Escherichia coli cytochrome d terminal oxidase complex, obtained by addition of excess hydrogen peroxide to the enzyme, is shown to be a ferryl intermediate in the catalytic cycle of the enzyme. This ferryl intermediate is also created by aerobic oxidation of the fully reduced enzyme. Resonance Raman spectra with 647.1-nm excitation show an FeIV = O stretching band at 815 cm-1, a higher frequency than noted in any other ferryl-containing enzyme to date. The band shows an 16O/18O frequency shift of -46 cm-1, larger than that observed for any porphyrin ferryl species. The FeIV = O formulation was unambiguously established by oxidations of the reduced enzyme with 16O2, 18O2, and 16O18O. Only the use of a mixed-isotope gas permitted discrimination between a ferryl and a peroxo structure. A catalytic cycle for the cytochrome d terminal oxidase complex is proposed, and possible reasons for the high v(Fe = O) frequency are discussed.
authors.affiliation: Department of Chemical and Biological Sciences, Oregon Graduate Institute of Science and Technology, Beaverton 97006-1999.
authors.forename: M A
authors.initials: MA
authors.lastname: Kahlow
authors.forename: T M
authors.initials: TM
authors.lastname: Zuberi
authors.forename: R B
authors.initials: RB
authors.lastname: Gennis
authors.forename: T M
authors.initials: TM
authors.lastname: Loehr
mesh_terms: D002384:Catalysis; D003573:Cytochrome b Group; D003580:Cytochromes; D045222:Electron Transport Chain Complex Proteins; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins; D006861:Hydrogen Peroxide / Q000737:chemistry; D007501:Iron / Q000032:analysis* / Q000737:chemistry; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry; D010103:Oxygen Isotopes; D013059:Spectrum Analysis, Raman
chemical_list: D003573:Cytochrome b Group; D003580:Cytochromes; D045222:Electron Transport Chain Complex Proteins; D029968:Escherichia coli Proteins; D010103:Oxygen Isotopes; C066317:ferryl iron; D006861:Hydrogen Peroxide; D007501:Iron; D010088:Oxidoreductases; C040077:cytochrome bd terminal oxidase complex, E coli; D010100:Oxygen