title: A kinetic study on the suicide inactivation of peroxidase by hydrogen peroxide.
abstract: In the absence of reductant substrates, and with excess H2O2, peroxidase (donor: hydrogen-peroxide oxidoreductase, EC 1.11.1.7) shows the kinetic behaviour of a suicide inactivation, H2O2 being the suicide substrate. From the complex (compound I-H2O2), a competition is established between two catalytic pathways (the catalase pathway and the compound III-forming pathway), and the suicide inactivation pathway (formation of inactive enzyme). A kinetic analysis of this system allows us to obtain a value for the inactivation constant, ki = (3.92 +/- 0.06) x 10(-3) x s-1. Two partition ratios (r), defined as the number of turnovers given by one mol of enzyme before its inactivation, can be calculated: (a) one for the catalase pathway, rc = 449 +/- 47; (b) the other for the compound III-forming pathway, rCoIII = 2.00 +/- 0.07. Thus, the catalase activity of the enzyme and, also, the protective role of compound III against an H2O2-dependent peroxidase inactivation are both shown to be important.
authors.affiliation: Departamento de Biología Vegetal (Fisología Vegetal), Universidad de Murcia, Spain.
authors.forename: M B
authors.initials: MB
authors.lastname: Arnao
authors.forename: M
authors.initials: M
authors.lastname: Acosta
authors.forename: J A
authors.initials: JA
authors.lastname: del Río
authors.forename: R
authors.initials: R
authors.lastname: Varón
authors.forename: F
authors.initials: F
authors.lastname: García-Cánovas
mesh_terms: D006735:Horseradish Peroxidase / Q000037:antagonists & inhibitors*; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D007700:Kinetics; D008433:Mathematics; D008962:Models, Theoretical; D011485:Protein Binding; D013053:Spectrophotometry
chemical_list: D006861:Hydrogen Peroxide; D006735:Horseradish Peroxidase