monophenol monooxygenase

1. A copper-containing oxidoreductase that catalyzes the oxidation of o-diphenols to o-quinones by O₂, with the incorporation of one of the two oxygen atoms in the product; it also catalyzes the oxidation of monophenols, such as l-tyrosine, to dihydroxy-l-phenylalanine (dopa), a precursor of melanin and epinephrine (catecholamines), and can act as a catechol oxidase; a deficiency of this enzyme is observed in a number of forms of albinism. SYN: cresolase, monophenol oxidase, tyrosinase. 2. SYN: laccase.

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mono·phe·nol mono·oxy·gen·ase (mon″o-feґnol mon″o-okґsĭ-jən-ās″) [EC 1.14.18.1] any of a group of enzymes of the oxidoreductase class that catalyze the hydroxylation of tyrosine to dopa and the oxidation of dopa to dopaquinone. They are copper proteins that also act on catechols and substituted catechols (i.e., act as catechol oxidases). The reaction is a step in the formation of melanin pigments from tyrosine. Cf. catechol oxidase.