Inactivation of Lipoxygenase by Hydrogen Peroxide, Cysteine and Some Other Reagents

Abstract

The polarographic data show that H2O2 is not formed during the course of the coupled oxidation of antioxidants by lipoxygenase from defatted soybean meal. A lower concentration of H2O2 or autoxidizing cysteine has been found to induce an irreversible inactivation of the enzyme. Inactivation activity of cysteine is reduced either by the addition of catalase or under anaerobic condition. These facts are indicative of the oxidative function of autoxidizing cysteine for the enzyme. The inactivation by cysteine and H2O2 respectively is in additive and is impeded by the addition of competitive inhibitors such as linolelaidic and conjugated linoleic acids, indicating a possible reaction with a certain amino acid residue involved in the enzymic catalysis. The experimental evidences obtained with H2O2 and some other modifying reagents have been integrated to furnish a basis of later identification of the residue that is exerting the specific catalytic function.