Tyrosinase is a rate-limiting enzyme in the melanin biosynthetic pathway and a complete defect of the enzyme activity caused by homozygous mutations of the tyrosinase gene is well known to result in tyrosinase-negative oculocutaneous albinism （OCA1A） patients who never develop any melanin pigment in the skin, hair and eyes throughout life （1）. Tyrosinase catalyzes the first two steps of melanin biosynthesis. Mutations of the TYR gene have been identified in a large number of patients, most of Caucasian ethnic origin, with various forms of type I OCA （2）. Type I OCA results from mutations of the gene encoding tyrosinase, the enzyme that catalyzes the first 2 steps of melanin pigment biosynthesis. In type IA （tyrosinase-negative） OCA tyrosinase enzymatic activity is compley absent, and in type IB （"yellow"） OCA tyrosinase activity is greatly reduced. More than 80% of the known missense substitutions associated with type I OCA cluster within 2 relatively small regions of the tyrosinase polypeptide, suggesting that these may correspond to functionally important sites within the enzyme （3）.

WB, IHC, FC, IP