Tyrosinase

• OMIM: 606 933
• UniProt: P14679

Tyrosinase is a copper-containing enzyme that catalyzes the oxidation of phenols, such as tyrosine catalysed. It is widely used in almost all living things.

In animals and human tyrosinase (along with the enzymes and TYRP1 DCT) involved in the synthesis of melanin in the melanocytes of the membrane, and therefore indispensable for the protection from UV radiation. In some of the organisms with albinism, the enzyme is altered or missing entirely. The tyrosinase in plants has additional functions and is called polyphenol oxidase.

Melanogenesis

The production of tyrosinase increases with increased UVB radiation. Then run to the cell membrane of melanoblasts following chemical reactions amplified from.

Tyrosine is first oxidized to L- dopa.

L- Dopa is further oxidized to dopaquinone which independently oxidized to dopachrome in two steps. From here a pathway in two steps using the enzymes TYRP1 and DCT for melanin is possible. However, the tyrosinase itself can also produce melanin from dopachrome:

Dopachrome is converted to 5,6- dihydroxyindole ( DHI).

DHI is oxidized to indole -5 ,6 -quinone, using oxygen which eventually polymerizes to melanin ( not shown).

It follows that tyrosinase is essential for the synthesis of melanin, whereas a lack of TYRP1 or DCT tyrosinase can be compensated for more or less. The amount of melanin produced is reduced in each case, so that there is a simple explanation for genetic variations in the color of skin, eyes and hair here.

Pathology

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

Albinism is generally associated with ophthalmic features such as nystagmus, strabismus, strong refractive defect, foveal dysgenesis, chorioretinal hypopigmentation. All mammals, which are known OCA1 a defect, have been in existence for only a OCA1 allele defects in the visual system that can not be explained by the amount of melanin produced, and its exact cause is still unknown. In one of these defects, a dysgenesis of the fovea centralis, no foveal depression is present, but the retina is as thick as everywhere else (300 microns compared to 150 microns ) in this area. Since an estimated one to two percent of people carry a heterozygous mutation in TYR, it is assumed that unexplained cases of blindness are due to stereo.