title: EPR and optical spectroscopic studies of Met80X mutants of yeast ferricytochrome c. Models for intermediates in the alkaline transition.
abstract: The ferric forms of Met80X mutants of yeast iso-1-cytochrome c (X = Ala, Ser, Asp, and Glu) display EPR and optical spectra that are strongly pH dependent. At low pH values (pH approximately 5) the sixth coordination sites are filled by H(2)O that, on elevating the pH, is replaced by OH(-) in the cases of Met80Ala and -Ser (pK approximately 5.6 and 5.9, respectively) and by a lysine amino group in the cases of Met80Asp and -Glu (pK approximately 9.3 and 11.6, respectively). The ligand sets and the pK values of the transitions are rationalized in terms of the structure of the heme pocket, and a possible mechanism of the "trigger" in the alkaline transition of the native protein is suggested.
authors.affiliation: Department of Biological Sciences, University of Essex, Wivenhoe Park, Colchester CO4 3SQ, Essex, UK.
authors.forename: Gary G
authors.initials: GG
authors.lastname: Silkstone
authors.forename: Christopher E
authors.initials: CE
authors.lastname: Cooper
authors.forename: Dimitri
authors.initials: D
authors.lastname: Svistunenko
authors.forename: Michael T
authors.initials: MT
authors.lastname: Wilson
mesh_terms: D045304:Cytochromes c / Q000737:chemistry* / Q000235:genetics; D004578:Electron Spin Resonance Spectroscopy; D005290:Ferric Compounds / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D011487:Protein Conformation; D012441:Saccharomyces cerevisiae / Q000737:chemistry; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry* / Q000235:genetics
chemical_list: C014059:CYC1 protein, S cerevisiae; D005290:Ferric Compounds; D029701:Saccharomyces cerevisiae Proteins; D045304:Cytochromes c