Tyrosinase (<db_xref db="EC" dbkey="1.14.18.1"/>) [<cite idref="PUB00004934"/>] is a copper monooxygenases that catalyzes thehydroxylation of monophenols and the oxidation of o-diphenols to o-quinols.This enzyme, found in prokaryotes as well as in eukaryotes, is involved in theformation of pigments such as melanins and other polyphenolic compounds.Tyrosinase binds two copper ions (CuA and CuB). Each of the two copper ions hasbeen shown [<cite idref="PUB00000492"/>] to be bound by three conserved histidines residues. The regionsaround these copper-binding ligands are well conserved and also shared by somehemocyanins, which are copper-containing oxygen carriers from the hemolymph ofmany molluscs and arthropods [<cite idref="PUB00004295"/>, <cite idref="PUB00004733"/>].At least two proteins related to tyrosinase are known to exist in mammals, and include TRP-1 (TYRP1) [<cite idref="PUB00001267"/>], which is responsible for the conversion of 5,6-dihydro-xyindole-2-carboxylic acid (DHICA) to indole-5,6-quinone-2-carboxylic acid; and TRP-2 (TYRP2) [<cite idref="PUB00001230"/>], which is the melanogenic enzyme DOPAchrome tautomerase (<db_xref db="EC" dbkey="5.3.3.12"/>) that catalyzes the conversion of DOPAchrome to DHICA. TRP-2 differs from tyrosinases and TRP-1 in that it binds two zinc ions instead of copper [<cite idref="PUB00000238"/>].Other proteins that belong to this family are plant polyphenol oxidases (PPO) (<db_xref db="EC" dbkey="1.10.3.1"/>), which catalyze the oxidation of mono- and o-diphenols to o-diquinones [<cite idref="PUB00004557"/>]; and <taxon tax_id="6239">Caenorhabditis elegans</taxon> hypothetical protein C02C2.1. Tyrosinase