Tyrosinase

Tyrosinase is a copper-containing enzyme that belongs to the polyphenol oxidase family. In humans and many other organisms, it catalyzes two related reactions in melanin biosynthesis: monophenolase activity converts the amino acid tyrosine to L-DOPA, and catecholase activity oxidizes L-DOPA to dopaquinone. These reactions initiate the production of melanin pigments in melanosomes.

In humans, tyrosinase is a key enzyme in pigment formation within melanocytes of the skin, hair, and eyes. After dopaquinone is formed, it undergoes further reactions that lead to eumelanin and pheomelanin, the two main types of melanin. The level and activity of tyrosinase, regulated at the transcriptional level by MITF and by post-translational processing, influence skin and hair color and tanning response.

Genetic mutations in the TYR gene can reduce or abolish tyrosinase activity, causing oculocutaneous albinism type 1. Patients show hypopigmentation of the skin, hair, and eyes, with potential vision problems. Other forms of albinism may involve related proteins such as TYRP1 and TYRP2.

Tyrosinase is also present in plants and other organisms as polyphenol oxidases that contribute to browning reactions when tissue is damaged. In the food industry and cosmetics, tyrosinase inhibitors, including kojic acid, hydroquinone, and arbutin, are used to prevent unwanted browning or to treat hyperpigmentation.

The enzyme contains a binuclear copper active site coordinated by histidine residues. It is synthesized as a precursor and matures in cellular organelles; in mammals it localizes to melanosomes and requires proper copper supply for activity.