türosinase

Türosinase, more commonly spelled tyrosinase, is a copper-containing oxidoreductase that catalyzes the first two steps of melanin biosynthesis. It converts the amino acid tyrosine to L-tyrosine–derived L-DOPA in a monophenolase reaction, and then oxidizes L-DOPA to dopaquinone in a diphenolase reaction. These reactions require molecular oxygen and two copper ions at the enzyme’s active site, and they proceed within melanosomes in melanocytes of the skin, hair, and retinal pigment epithelium.

The enzyme is encoded by the TYR gene. TYR expression is regulated by transcription factors such as MITF and is subject to developmental and environmental signals. Biochemically, tyrosinase is synthesized as a precursor protein, glycosylated, and trafficked through the endoplasmic reticulum and Golgi to melanosomes, where its activity is optimized by the organelle’s pH and other maturation steps. In humans, tyrosinase activity is a key determinant of eumelanin production, contributing to dark pigmentation, while its activity, along with other related enzymes, also influences pheomelanin synthesis.

Clinical and biomedical relevance includes its role in oculocutaneous albinism type 1, where TYR mutations reduce or abolish enzyme activity, leading to hypopigmentation and vision problems. Tyrosinase is also a target in cosmetic and dermatological applications, with inhibitors such as kojic acid and hydroquinone used to treat hyperpigmentation. In oncology research, tyrosinase is recognized as a melanoma-associated antigen and has been explored in immunotherapeutic approaches. Related enzymes, TYRP1 and TYRP2, participate downstream in melanin synthesis and share functional ties with tyrosinase.