title: Kinetics of the reaction of superoxide anion with ferric horseradish peroxidase.
abstract: Reaction of horseradish peroxidase A2 and C with superoxide anion (O2-) has been studied using pulse radiolysis technique. Peroxidase C formed Compound I and an oxy form of the enzyme due to reaction of ferric enzyme with hydrogen peroxide (H2O2) and O2-, respectively. At low concentrations of O2- (less than 1 mM), O2- reacted with ferric peroxidase C nearly quantitatively and formation of H2O2 was negligible. The rate constant for the reaction was found to be increased below pH 6 and this phenomenon can be explained by assuming that HO2 reacts with peroxidase C more rapidly than O2-. In contrast the formation of oxyperoxidase could not be detected in the case of peroxidase A2 after the pulse, and only Compound I of the enzyme was formed. Peroxidase A2, however, produced the oxy form upon aerobic addition of NADH, suggesting that O2- can also react with peroxidase A2 to form the oxy form. The results at present indicate that the rate constant for the reaction of O2- with peroxidase A2 is smaller than 103 M-1.s-1.
authors.affiliation: Institute of Scientific and Industrial Research Osaka University, Japan.
authors.forename: N
authors.initials: N
authors.lastname: Shimizu
authors.forename: K
authors.initials: K
authors.lastname: Kobayashi
authors.forename: K
authors.initials: K
authors.lastname: Hayashi
mesh_terms: D006735:Horseradish Peroxidase / Q000378:metabolism*; D006861:Hydrogen Peroxide / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007527:Isoenzymes / Q000378:metabolism; D007700:Kinetics; D010544:Peroxidases / Q000378:metabolism*; D011675:Pulse Radiolysis; D013481:Superoxides / Q000378:metabolism*
chemical_list: D007527:Isoenzymes; D013481:Superoxides; D006861:Hydrogen Peroxide; D006735:Horseradish Peroxidase; D010544:Peroxidases