ABSTRACT
Polyphenol oxidase is frequently called tyrosinase, polyphenolase, phenolase, catechol oxidase, cresolase, or catecholase. Polyphenol oxidase is present in animals, including humans, where it is important for skin, hair, and eye pigmentation. Polyphenol oxidase is also important in formation of the exoskeleton of insects. Polyphenol oxidase is of great importance in determining the quality attributes of some fruits and vegetables. Unlike most enzymes, polyphenol oxidase can catalyze two quite different types of reactions, both of which involve phenolic compounds. Peach and broad bean polyphenol oxidases differ in their relative activities on protocatechuic acid, gallic acid, and four-methylcatechol. A. Golan-Goldhirsh et al. showed that ascorbic acid has a direct effect on polyphenol oxidase, especially in the presence of micromolar copper ions. Relatively little is known about the protein nature of the fruit and vegetable polyphenol oxidases. Neurospora crassa polyphenol oxidase is much easier to study because it is easily purified, unlike the ones from mushrooms, and occurs in only one isoform.
