an enzyme, found in plants and animals, that catalyzes the oxidation of the amino acid tyrosine and is involved in the formation of the dark pigment melanin
See tyrosinase in American Heritage Dictionary 4
(tī-rŏsˈə-nāsˌ, -nāzˌ)
noun
A copper-containing enzyme of plant and animal tissues that catalyzes the production of melanin and other pigments from tyrosine by oxidation, as in the blackening of a peeled or sliced potato exposed to air.