title: Catalase-like activity of horseradish peroxidase: relationship to enzyme inactivation by H2O2.
abstract: H2O2 is the usual oxidizing substrate of horseradish peroxidase C (HRP-C). In the absence in the reaction medium of a one-electron donor substrate, H2O2 is able to act as both oxidizing and reducing substrate. However, under these conditions the enzyme also undergoes a progressive loss of activity. There are several pathways that maintain the activity of the enzyme by recovering the ferric form, one of which is the decomposition of H2O2 to molecular oxygen in a similar way to the action of catalase. This production of oxygen has been kinetically characterized with a Clark-type electrode coupled to an oxygraph. HRP-C exhibits a weak catalase-like activity, the initial reaction rate of which is hyperbolically dependent on the H2O2 concentration, with values for K(2) (affinity of the first intermediate, compound I, for H2O2) and k(3) (apparent rate constant controlling catalase activity) of 4.0 +/- 0.6 mM and 1.78 +/- 0.12 s(-1) respectively. Oxygen production by HRP-C is favoured at pH values greater than approx. 6.5; under similar conditions HRP-C is also much less sensitive to inactivation during incubations with H2O2. We therefore suggest that this pathway is a major protective mechanism of HRP-C against such inactivation.
authors.affiliation: Departamento de Biología Vegetal (Fisiología Vegetal), Universidad de Murcia, E-30100 Espinardo, Murcia, Spain.
authors.forename: J
authors.initials: J
authors.lastname: Hernández-Ruiz
authors.forename: M B
authors.initials: MB
authors.lastname: Arnao
authors.forename: A N
authors.initials: AN
authors.lastname: Hiner
authors.forename: F
authors.initials: F
authors.lastname: García-Cánovas
authors.forename: M
authors.initials: M
authors.lastname: Acosta
mesh_terms: D002374:Catalase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006735:Horseradish Peroxidase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D007700:Kinetics; D010100:Oxygen / Q000378:metabolism
chemical_list: D004791:Enzyme Inhibitors; D006861:Hydrogen Peroxide; D006735:Horseradish Peroxidase; D002374:Catalase; D010100:Oxygen