Effects of an abundant human skin melanosomal 66 kDa protein (MP 66) on murine tyrosinase: Its physiological implications on melanogenesis.

A single polypeptide protein (MP 66) of molecular weight 66 kDa purified to homogeneity from melanosomes of normal human skin epidermal melanocytes, was partially characterized. The isoelectric point of MP 66 is in the range of 7.3 to 7.6. This protein, which was shown to inhibit partially purified human skin tyrosinase activity at pH 6.8, also inhibits murine tyrosinase at pH 6.8. However, at pH 5.0, it stimulates murine tyrosinase activity. The physiological implications of these results are discussed.