title: Cytochrome c and cytochrome c oxidase interactions: the effects of ionic strength and hydrostatic pressure studied with site-specific modifications of cytochrome c.
abstract: Seven cytochromes c, in which individual lysines have been modified to the propylthiobimane derivatives, have been prepared. These derivatives were also converted to the porphyrin cytochromes c by treatment with HF. The properties of both types of modified proteins were studied in their reactions with cytochrome c oxidase. The results show that lysines 25, 27, 60, 72, and 87 do not contribute a full charge to the binding interaction with the oxidase. These five residues, with the exception of the lysine-60 derivative, on the front surface of the protein and contain the solvent-accessible edge of the heme prosthetic group. By contrast, lysines 8 and 13 at the top of the front surface do contribute a full charge to the binding interaction with the oxidase. The removal of the positive charge on any one lysine weakens the binding to cytochrome c oxidase by at least 1 kcal (1 cal = 4.1868 J). The presence of bimane at lysines 13 and 87 clearly forces the separation of the cytochrome c and oxidase, but this does not occur with the other complexes. The bimane-modified lysine-13 protein, and to a lesser extent that modified at lysine 8, show the interesting effect of enhanced complex formation with cytochrome c oxidase when subjected to pressure, possibly because of entrapment of water at the newly created interface of the complex. Our observations indicate that the two proteins of the cytochrome c - cytochrome oxidase complex have preferred, but not obligatory, spatial orientations and that interaction occurs without either protein losing significant portions of its hydration shell.
authors.affiliation: Department of Biology, Concordia University, Montréal, Que., Canada.
authors.forename: J A
authors.initials: JA
authors.lastname: Kornblatt
authors.forename: J
authors.initials: J
authors.lastname: Theodorakis
authors.forename: G H
authors.initials: GH
authors.lastname: Hoa
authors.forename: E
authors.initials: E
authors.lastname: Margoliash
mesh_terms: D000818:Animals; D002417:Cattle; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003574:Cytochrome c Group / Q000235:genetics / Q000378:metabolism*; D004579:Electron Transport; D003576:Electron Transport Complex IV / Q000378:metabolism*; D006736:Horses; D006874:Hydrostatic Pressure; D016297:Mutagenesis, Site-Directed; D009994:Osmolar Concentration; D013379:Substrate Specificity
chemical_list: D003574:Cytochrome c Group; D003576:Electron Transport Complex IV