Zymography of monophenolase and o-diphenolase activities of polyphenol oxidase.

Polyphenol oxidase (PPO) (monophenol, o-diphenol: oxygen oxidoreductase; EC 1.14.18.1) is a binuclear copper-cluster-containing monooxygenase ubiquitously present in biological systems (1, 2). PPO may be distinguished from the related oxidase laccase [p-diphenol:oxygen oxidoreductase; EC 1.10.3.2] by its substrate specificity and the type and number of catalytic coppers. PPO catalyzes the oxidation of o-diphenols (o-diphenolase or catecholase activity) to the corresponding o-quinones, by consumption of molecular oxygen. It may also catalyze the regioselective orthohydroxylation of monophenols to catechols and their subsequent oxidation to o-quinones (monophenolase or cresolase activity). The resulting quinones may undergo nonenzymatic autopolymerization or covalent heterocondensation with proteins to produce colored compounds (1). Peroxidases (POXs) (donor:hydrogen