Biochemistry of melanin synthesis: in vivo effects of MSH on tyrosinase and melanogenesis of pigmentary system.

Melanogenesis is a process which forms new pigment and is considered to have the function of controlling the overall pigmentation of higher animals, including man. An enhancement of melanogenesis is observed when a prolonged in vivo administration of melanocyte-stimulating hormone (MSH) is given to test animals. The mechanism through which MSH induces melanogenesis in vivo is not well understood at present. Since tyrosinase is a key enzyme involved in biosynthesis of melanin pigment and is present in appreciable quantities in pigmentary system, it seems likely that it participates in the action of MSH on pigment formation. This communication reports the in vivo effect of MSH on tyrosinase activity and melanogenesis of two different pigmentary systems, namely, the benign skin melanocytes of Rana pipiens frog and malignant B-16 mouse melanoma. A uniform hypothesis on the mechanism of induction of melanogenesis by this hormone is postulated.