title: Oxidation of yeast iso-1 ferrocytochrome c by yeast cytochrome c peroxidase compounds I and II. Dependence upon ionic strength.
abstract: The reduction of cytochrome c peroxidase compound I by excess yeast iso-1 ferrocytochrome c is biphasic. Two pseudo-first-order rate constants can be measured by stopped-flow techniques. The fastest rate process is the reduction of cytochrome c peroxidase compound I to compound II, and the slower process is the reduction of II to the native enzyme. The yeast iso-1 ferrocytochrome c concentration dependence of the reduction of cytochrome c peroxidase compound I to compound II is consistent with a mechanism involving two binding sites for cytochrome c on cytochrome c peroxidase. Electron transfer from cytochrome c bound at the high-affinity binding site to the Fe(IV) site in cytochrome c peroxidase compound I is dependent upon ionic strength, increasing from 15 +/- 6 to 2000 +/- 100 s-1 over the ionic strength range 0.01-0.20 M. The reduction rate of the Fe(IV) site in the 2:1 yeast iso-1 ferrocytochrome c/cytochrome c peroxidase compound I complex is essentially independent of ionic strength with a value of 3800 +/- 300 s-1. The Fe(IV) site in cytochrome c peroxidase compound I is preferentially reduced by yeast ferrocytochrome c between 0.01 and 0.20 M ionic strength while the Trp-191 radical is preferentially reduced above 0.30 M ionic strength. The association rate constant for the binding of yeast iso-1 ferrocytochrome c to cytochrome c peroxidase compound I can be evaluated and varies from a remarkable 1 x 10(10) M-1 s-1 at 0.01 M ionic strength to 1.2 x 10(5) M-1 s-1 at 1.0 M ionic strength. Between 0.01 and 0.20 M ionic strength, the reduction of cytochrome c peroxidase compound II to the native enzyme is anomalous. The reaction is independent of the cytochrome c concentration and directly proportional to the initial cytochrome c peroxidase compound I concentration.
authors.affiliation: Department of Chemistry, Northern Illinois University, DeKalb 60115, USA.
authors.forename: A L
authors.initials: AL
authors.lastname: Matthis
authors.forename: L B
authors.initials: LB
authors.lastname: Vitello
authors.forename: J E
authors.initials: JE
authors.lastname: Erman
mesh_terms: D001665:Binding Sites; D003574:Cytochrome c Group / Q000378:metabolism*; D003578:Cytochrome-c Peroxidase / Q000378:metabolism*; D045304:Cytochromes c; D017022:Flow Injection Analysis; D005609:Free Radicals / Q000378:metabolism; D007501:Iron / Q000378:metabolism; D007700:Kinetics; D008956:Models, Chemical; D009994:Osmolar Concentration; D010084:Oxidation-Reduction; D012441:Saccharomyces cerevisiae / Q000201:enzymology; D029701:Saccharomyces cerevisiae Proteins
chemical_list: C014059:CYC1 protein, S cerevisiae; D003574:Cytochrome c Group; D005609:Free Radicals; D029701:Saccharomyces cerevisiae Proteins; D045304:Cytochromes c; D007501:Iron; D003578:Cytochrome-c Peroxidase