title: The reaction of Aspergillus niger catalase with methyl hydroperoxide.
abstract: The formation of Compound I from Aspergillus niger catalase and methyl hydroperoxide (CH3OOH) has been investigated kinetically by means of rapid-scanning stopped-flow techniques. The spectral changes during the reaction showed distinct isobestic points. The second-order rate constant and the activation energy for the formation of Compound I were 6.4 x 10(3) M-1s-1 and 10.4 kcal.mol-1, respectively. After formation of Compound I, the absorbance at the Soret peak returned slowly to the level of ferric enzyme with a first-order rate constant of 1.7 x 10(-3) s-1. Spectrophotometric titration of the enzyme with CH3OOH indicates that 4 mol of peroxide react with 1 mol of enzyme to form 1 mol of Compound I. The amount of Compound I formed was proportional to the specific activity of the catalase. The irreversible inhibition of catalase by 3-amino-1,2,4-triazole (AT) was observed in the presence of CH3OOH or H2O2. The second-order rate constant of the catalase-AT formation in CH3OOH was 3.0 M-1 min-1 at 37 degrees C and pH 6.8 and the pKa value was estimated to be 6.10 from the pH profile of the rate constant of the AT-inhibition. These results indicate that A. niger catalase forms Compound I with the same properties as other catalases and peroxidases, but the velocity of the Compound I formation is lower than that of the others.
authors.affiliation: Department of Biophysical Chemistry, Kitasato University School of Medicine, Kanagawa, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Kikuchi
authors.forename: Y
authors.initials: Y
authors.lastname: Kawamura-Konishi
authors.forename: H
authors.initials: H
authors.lastname: Suzuki
mesh_terms: D000818:Animals; D001234:Aspergillus niger / Q000201:enzymology*; D002374:Catalase / Q000097:blood / Q000378:metabolism*; D004912:Erythrocytes / Q000201:enzymology; D006736:Horses; D006801:Humans; D007700:Kinetics; D008837:Micrococcus / Q000201:enzymology; D010545:Peroxides / Q000378:metabolism*; D011485:Protein Binding; D013053:Spectrophotometry; D013997:Time Factors
chemical_list: D010545:Peroxides; D002374:Catalase