Oxidation of 2-nitropropane by horseradish peroxidase. Involvement of hydrogen peroxide and of superoxide in the reaction mechanism

Abstract

Incubation of aqueous solutions of 2-nitropropane in air causes a slow oxidation reaction that generates H2O2. Purified horseradish peroxidase catalyses the oxidation of such preincubated 2-nitropropane solutions according to the equation: [Formula: see text] The pH optimum is 4.5 and Km for 2-nitropropane is 16mm. Other nitroalkanes or nitro-aromatics tested are not oxidized at significant rates by peroxidase. H2O2 or 2,4-dichlorophenol increases the rate of 2-nitropropane oxidation by peroxidase. Catalase inhibits the reaction completely. Superoxide dismutase or mannitol, a scavenger of the hydroxyl radical, OH., each inhibits partially. Aniline and guaiacol are also powerful inhibitors of 2-nitropropane oxidation. It is suggested that peroxidase uses the traces of H2O2 generated during preincubation of 2-nitropropane to catalyse oxidation of this substrate into a radical species that can reduce O2 to the superoxide ion, O2−..O2−., or OH. derived from it, then appears to react with more nitropropane, generating further radicals and H2O2 to continue the oxidation. Inhibition by aniline and guaiacol seems to be due to a competition for H2O2.