title: Cytochrome c binding affects the conformation of cytochrome a in cytochrome c oxidase.
abstract: Second derivative absorption spectroscopy has been used to assess the effects of complex formation between cytochrome c and cytochrome c oxidase on the conformation of the cytochrome a cofactor. When ferrocytochrome c is complexed to the cyanide-inhibited reduced or mixed valence enzyme, the conformation of ferrocytochrome a is affected. The second derivative spectrum of these enzyme forms displays two electronic transitions at 443 and 451 nm before complex formation, but only the 443-nm transition after cytochrome c is bound. This effect is not induced by poly-L-lysine, a homopolypeptide which is known to bind to the cytochrome c binding domain of cytochrome c oxidase. The effect is limited to cyanide-inhibited forms of the enzyme; no effect was observed for the fully reduced unliganded or fully reduced carbon monoxide-inhibited enzyme. The spectral signatures of these changes and the fact that they are exclusively associated with the cyanide-inhibited enzyme are both reminiscent of the effects of low pH on the conformation of cytochrome a (Ishibe, N., Lynch, S., and Copeland, R. A. (1991) J. Biol. Chem. 266, 23916-23920). These results are discussed in terms of possible mechanisms of communication between the cytochrome c binding site, cytochrome a, and the oxygen binding site within the cytochrome c oxidase molecule.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Chicago, Illinois 60637.
authors.forename: S R
authors.initials: SR
authors.lastname: Lynch
authors.forename: D
authors.initials: D
authors.lastname: Sherman
authors.forename: R A
authors.initials: RA
authors.lastname: Copeland
mesh_terms: D000818:Animals; D002417:Cattle; D003486:Cyanides / Q000494:pharmacology; D003574:Cytochrome c Group / Q000378:metabolism*; D003576:Electron Transport Complex IV / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*; D010084:Oxidation-Reduction; D011487:Protein Conformation; D013059:Spectrum Analysis, Raman
chemical_list: D003486:Cyanides; D003574:Cytochrome c Group; D003576:Electron Transport Complex IV