title: Kinetic studies on [methionine sulphoxide] cytochrome c.
abstract: A cytochrome c haem ligand, methionine-80, was photo-oxidized to methionine sulphoxide and the subsequent changes in redox properties and ligand binding were monitored kinetically. Isoelectric focusing of the product showed the presence of a single oxidized species, capable of binding CO when reduced. The binding of CO to the reduced protein was followed in stopped-flow experiments, which revealed the presence of two binding processes, at neutral pH, with rate constants of K+1 = 3.4 X 10(3)M-1-S-1 and k+2 = 5.80 X 10(2)M-1-S-1. When CO was photolytically dissociated from the reduced protein two recombination processes were observed with rates almost identical with those observed in the stopped-flow experiments (k+1 = 3.3 X 10(3)M-1-S-1 and k+2 = 6.0 X 10(2)M-1-S-1). These findings provide evidence of two reduced forms of the protein. The reduction of [methionine sulphoxide]cytochrome c by Cr2+ at neutral pH in stopped-flow experiments showed the presence of a single second-order reduction process (k = 7.2 X 10(3)M-1-S-1, activation energy = 44kJ/mol) and one first-order process. This protein was compared with some other chemically modified cytochromes.
mesh_terms: D002248:Carbon Monoxide; D003574:Cytochrome c Group; D004579:Electron Transport; D007525:Isoelectric Focusing; D007700:Kinetics; D008024:Ligands; D008715:Methionine / Q000031:analogs & derivatives; D010084:Oxidation-Reduction; D011485:Protein Binding; D013454:Sulfoxides
chemical_list: D003574:Cytochrome c Group; D008024:Ligands; D013454:Sulfoxides; D002248:Carbon Monoxide; D008715:Methionine