title: The reaction of hydrogen peroxide with the dimethyl ester heme derivative of cytochrome c peroxidase.
abstract: A modified cytochrome c peroxidase was prepared by reconstituting apocytochrome c peroxidase with protoheme in which both heme propionic acid groups were converted to the methyl ester derivatives. The modified enzyme reacted with hydrogen peroxide with a rate constant of (1.3 +/- 0.2) x 10(7) M-1 s-1, which is 28% that of the native enzyme. The reaction between the modified enzyme and hydrogen peroxide was pH-dependent with an apparent pK of 5.1 +/- 0.1 compared to a value of 5.4 +/- 0.1 for the native enzyme. These observations support the conclusion that the apparent ionization near pH 5.4, which influences the hydrogen peroxide-cytochrome c peroxidase reaction is not due to the ionization of the propionate side chains of the heme group in the native enzyme. A second apparent ionization, with pK of 6.1 +/- 0.1, influences the spectrum of the modified enzyme which changes from a high spin type at low pH to a low spin type at high pH.
mesh_terms: D001051:Apoenzymes / Q000378:metabolism; D003578:Cytochrome-c Peroxidase / Q000378:metabolism*; D006418:Heme / Q000031:analogs & derivatives; D006861:Hydrogen Peroxide; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D010544:Peroxidases / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000201:enzymology; D013053:Spectrophotometry
chemical_list: D001051:Apoenzymes; D006418:Heme; D006861:Hydrogen Peroxide; D010544:Peroxidases; D003578:Cytochrome-c Peroxidase