title: Structural characterization of a binuclear center of a Cu-containing NO reductase homologue from Roseobacter denitrificans: EPR and resonance Raman studies.
abstract: Aerobic phototrophic bacterium Roseobacter denitrificans has a nitric oxide reductase (NOR) homologue with cytochrome c oxidase (CcO) activity. It is composed of two subunits that are homologous with NorC and NorB, and contains heme c, heme b, and copper in a 1:2:1 stoichiometry. This enzyme has virtually no NOR activity. Electron paramagnetic resonance (EPR) spectra of the air-oxidized enzyme showed signals of two low-spin hemes at 15 K. The high-spin heme species having relatively low signal intensity indicated that major part of heme b3 is EPR-silent due to an antiferromagnetic coupling to an adjacent CuB forming a Fe-Cu binuclear center. Resonance Raman (RR) spectrum of the oxidized enzyme suggested that heme b3 is six-coordinate high-spin species and the other hemes are six-coordinate low-spin species. The RR spectrum of the reduced enzyme showed that all the ferrous hemes are six-coordinate low-spin species. Nu(Fe-CO) and nu(C-O) stretching modes were observed at 523 and 1969 cm(-1), respectively, for CO-bound enzyme. In spite of the similarity to NOR in the primary structure, the frequency of nu(Fe-CO) mode is close to those of aa3- and bo3-type oxidases rather than that of NOR.
authors.affiliation: Department of Biology, Graduate School of Sciences, Kyushu University, 6-10-1 Hakozaki, Higashi, Fukuoka 812-8581, Japan.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Matsuda
authors.forename: Takeshi
authors.initials: T
authors.lastname: Uchida
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Hori
authors.forename: Teizo
authors.initials: T
authors.lastname: Kitagawa
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Arata
mesh_terms: D003300:Copper / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D003576:Electron Transport Complex IV / Q000737:chemistry; D055095:Optics and Photonics; D010088:Oxidoreductases / Q000737:chemistry* / Q000378:metabolism; D041904:Roseobacter / Q000201:enzymology*; D013059:Spectrum Analysis, Raman; D040681:Structural Homology, Protein
chemical_list: D003300:Copper; D010088:Oxidoreductases; C034747:nitric-oxide reductase; D003576:Electron Transport Complex IV