title: Cyanide-binding site of bd-type ubiquinol oxidase from Escherichia coli.
abstract: We extended our investigation on the structure of the redox centers of bd-type ubiquinol oxidase from Escherichia coli using cyanide as a monitoring probe. We found that addition of cyanide to the air-oxidized O2-bound enzyme caused appearance of an infrared C-N stretching band at 2161 cm-1 and concomitant disappearance of the 647 nm absorption band of the cytochrome d (Fe2+)-O2 species. Addition of cyanide to the air-oxidized CO-bound enzyme also resulted in disappearance of the 635 nm absorption band and the 1983.4 cm-1 C-O infrared band of the cytochrome d (Fe2+)-CO species. The resulting species had a derivative-shaped electron paramagnetic resonance signal at g = 3.15. Upon partial reduction with sodium dithionite, this species was converted partly to a transient heme d (Fe3+)-C = N species having an electron paramagnetic resonance signal at gz = 2.96 and a C-N infrared band at 2138 cm-1. These observations suggest that the active site of the enzyme has a heme-heme binuclear metal center distinct from that of the heme-copper terminal oxidase and that the treatment of the air-oxidized enzyme with cyanide resulted in a cyanide-bridging species with "heme d(Fe3+)-C = N-heme b595(Fe3+)" structure.
mesh_terms: D001665:Binding Sites; D003486:Cyanides / Q000378:metabolism*; D003573:Cytochrome b Group; D003580:Cytochromes / Q000737:chemistry / Q000378:metabolism*; D045222:Electron Transport Chain Complex Proteins; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins; D006418:Heme / Q000032:analysis; D008670:Metals / Q000032:analysis; D010088:Oxidoreductases / Q000737:chemistry / Q000378:metabolism*; D013057:Spectrum Analysis
chemical_list: D003486:Cyanides; D003573:Cytochrome b Group; D003580:Cytochromes; D045222:Electron Transport Chain Complex Proteins; D029968:Escherichia coli Proteins; D008670:Metals; D006418:Heme; D010088:Oxidoreductases; C040077:cytochrome bd terminal oxidase complex, E coli