Tyrosinase

Tyrosinase is a copper-containing protein (enzyme - oxidoreductase) with 529 amino acids, which is widely distributed in plants and animals. In humans, tyrosinase is involved in the synthesis of melanin. It is activated by UV light. The coding human tyrosinase gene (TYRP-1 gene) is located on the long arm of chromosome 11 (11q14-21).

The biosynthesis of melanin begins with the hydroxylation of the amino acid LTyrosine to dihydroxyphenylalanine (Dopa) and the oxidation of Dopa to Dopaquinone. These reactions are catalysed by the enzyme tyrosinase, which is the speed determining enzyme of the whole reaction.

The differentiated, melanin-loaded pigment polymer is deposited on a protein matrix within the melanosomes. In the skin and hair, the melanosomes are then transported via the dendrites of the melanocytes to the keratinocytes. In the keratinocytes, the melanosomes are stored in the form of a cap on the side of the cell nucleus facing the skin surface. The cell nucleus and the DNA in it are thus protected from the harmful effects of UV radiation.

Mutations in the TYR gene are responsible for oculocutaneous albinism type 1 (OCA1). A variant of Waardenburg syndrome type 2 is caused by an interaction of a mutation of the tyrosinase locus (R402Q) with a mutation of the Mitf gene.

Copper deficiency (Menkes syndrome) therefore leads to reduced enzyme formation and reduced pigmentation.

Glutathione has been shown to inhibit the activity of tyrosinase.

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