title: Thermodynamics of the equilibrium unfolding of oxidized and reduced Saccharomyces cerevisiae iso-1-cytochromes c.
abstract: We report thermodynamic data for the chemical denaturation of iso-1-cytochromes c from Saccharomyces cerevisiae having amino acid substitutions R38A, N52I, and F82S in all possible combinations. The guanidine hydrochloride denaturation of isolated proteins was monitored by fluorescence measurements. The redox potentials, Eo', for both the folded and unfolded conformations have been measured. Free energy changes of chemical unfolding together with direct electrochemical measurement of the free energy changes of reduction for both the native and unfolded proteins yield a complete thermodynamic cycle, which includes four states of cytochrome c: oxidized folded, oxidized unfolded, reduced folded, and reduced unfolded. Completed cycles illustrate that the stability of cytochrome c to denaturing conditions is different for each amino acid substitution by an amount that depends on the heme oxidation state. Thus, the differential protein stability cannot be interpreted simply in terms of a hydrophobic effect, without also considering coupled Coulombic effects.
authors.affiliation: Department of Chemistry, University of Rochester, New York 14627.
authors.forename: S
authors.initials: S
authors.lastname: Komar-Panicucci
authors.forename: D
authors.initials: D
authors.lastname: Weis
authors.forename: G
authors.initials: G
authors.lastname: Bakker
authors.forename: T
authors.initials: T
authors.lastname: Qiao
authors.forename: F
authors.initials: F
authors.lastname: Sherman
authors.forename: G
authors.initials: G
authors.lastname: McLendon
mesh_terms: D001483:Base Sequence; D003574:Cytochrome c Group / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D045304:Cytochromes c; D004271:DNA, Fungal / Q000235:genetics; D005800:Genes, Fungal; D006418:Heme / Q000737:chemistry; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010084:Oxidation-Reduction; D017510:Protein Folding; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D013816:Thermodynamics
chemical_list: C014059:CYC1 protein, S cerevisiae; D003574:Cytochrome c Group; D004271:DNA, Fungal; D029701:Saccharomyces cerevisiae Proteins; D006418:Heme; D045304:Cytochromes c