title: pH-Dependent peroxidase activity of yeast cytochrome c and its triple mutant adsorbed on kaolinite.
abstract: The peroxidase activity of wild-type yeast cytochrome c and its triple mutant K72AK73AK79A adsorbed onto kaolinite was investigated as a function of pH and temperature. Both adsorbed proteins displayed an appreciable catalytic activity, which remained constant from pH 7 to pH 10, decreased below pH 7, and showed a remarkable increase at pH values lower than 4. In the whole pH range investigated the catalytic activity of the adsorbed wild-type cytochrome c was higher than that of the mutant. Both diffuse-reflectance UV-vis and resonance Raman spectroscopies applied on solid samples were used to probe the structural features responsible for the catalytic activity of the immobilized proteins. At neutral and alkaline pH values a six-coordinate low-spin form of cytochrome c was observed, while at pH < 7 the formation of a high-spin species occurred whose population increased at decreasing pH. The orientation and exposure of the heme to the substrate-strictly dependent on adsorption-was found to affect the peroxidase activity.
authors.affiliation: Department of Chemistry, University of Modena and Reggio Emilia, Via Campi 183, I-41125 Modena, Italy.
authors.forename: Antonio
authors.initials: A
authors.lastname: Ranieri
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Bernini
authors.forename: Carlo Augusto
authors.initials: CA
authors.lastname: Bortolotti
authors.forename: Alois
authors.initials: A
authors.lastname: Bonifacio
authors.forename: Valter
authors.initials: V
authors.lastname: Sergo
authors.forename: Elena
authors.initials: E
authors.lastname: Castellini
mesh_terms: D000327:Adsorption; D045304:Cytochromes c / Q000378:metabolism*; D004789:Enzyme Activation; D006863:Hydrogen-Ion Concentration; D007616:Kaolin / Q000737:chemistry*; D009154:Mutation; D009195:Peroxidase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000378:metabolism; D013499:Surface Properties
chemical_list: D007616:Kaolin; D045304:Cytochromes c; D009195:Peroxidase