title: Spontaneous spectral changes of the reduced cytochrome bd.
abstract: Reduction of the membrane-bound cytochrome bd from Bacillus subtilis, Escherichia coli and Azotobacter vinelandii as well as of the purified enzyme from E. coli was followed by secondary absorption changes on a time scale of tens of minutes. The difference absorption spectra of these changes resembled those induced by CO binding with heme d2+ indicating interaction of the heme with an endogenous pi-acceptor ligand. The spontaneous spectral changes were prevented and reversed by CO binding with the reduced cytochrome bd. Bonding of heme d iron to an endogenous protein ligand at the sixth axial position upon reduction is proposed and several possible mechanisms of such a process are considered.
authors.affiliation: A.N. Belozerskiy Institute of Physico-Chemical Biology, Moscow State University, Russia.
authors.forename: N
authors.initials: N
authors.lastname: Azarkina
authors.forename: V
authors.initials: V
authors.lastname: Borisov
authors.forename: A A
authors.initials: AA
authors.lastname: Konstantinov
mesh_terms: D016948:Azotobacter vinelandii / Q000201:enzymology; D001412:Bacillus subtilis / Q000201:enzymology / Q000235:genetics; D001665:Binding Sites; D002248:Carbon Monoxide / Q000494:pharmacology; D003573:Cytochrome b Group; D003580:Cytochromes / Q000737:chemistry* / Q000378:metabolism*; D004227:Dithionite / Q000494:pharmacology; D045222:Electron Transport Chain Complex Proteins; D004926:Escherichia coli / Q000201:enzymology; D029968:Escherichia coli Proteins; D006418:Heme / Q000378:metabolism; D007501:Iron / Q000378:metabolism; D007700:Kinetics; D008956:Models, Chemical; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000737:chemistry* / Q000378:metabolism*; D013053:Spectrophotometry / Q000379:methods
chemical_list: D003573:Cytochrome b Group; D003580:Cytochromes; D045222:Electron Transport Chain Complex Proteins; D029968:Escherichia coli Proteins; D004227:Dithionite; D006418:Heme; D002248:Carbon Monoxide; D007501:Iron; D010088:Oxidoreductases; C040077:cytochrome bd terminal oxidase complex, E coli