A copper-containing enzyme that catalyzes the o-hydroxylation of monophenols to o-diphenols, as well as the oxidation of o-diphenols to o-quinones.
This enzyme is found commonly in fruits. It is responsible for the fruits to turn brown. The rapid polymerization of o-quinones results in the formation of black, brown, or red pigments (polyphenols), which cause fruit browning.
Tyrosine may also be oxidized by the action of polyphenol oxidase to form o-quinone. Hence, polyphenol oxidase may also be referred to as tyrosinase.
Word origin: Greek, polýs, many + phenol.
See also: phenol oxidase.