It is generally assumed that tyrosine is the precursor of melanin formed in human skin (Lerner and Fitzpatrick, 1950). The specific enzyme for melanogenesis, tyrosinase, is thought to be located in the melanocytes or pigmentory dendritic cells of the epidermis (Masson, 1948; Billingham, 1948 and 1949; Becker Jr., Fitzpatrick, and Montgomery, 1952; Billingham and Medawar, 1953).
Histochemical localization of tyrosinase in melanocytes of mammalian skin, however, has been unsuccessful but for two instances. Foster (1952) and Foster and Cook (1954) have found a positive reaction in the melanocytes of the hair follicles of mice, and Fitzpatrick, Becker Jr., Lerner and Montgomery (1950) and Fitzpatrick (1952) demonstrated the uptake of tyrosine in melanomas and in irradiated epidermis of human skin. Melanocytes of normal, nonirradiated epidermis of the same skin failed to take up tyrosine and to form pigment. Similar results were obtained
SZABÓ G. Tyrosinase in the Epidermal Melanocytes of White Human Skin: The Histochemical Demonstration and the Numerical Relationship of Tyrosine-Positive and Dopa-Positive Cells. AMA Arch Derm. 1957;76(3):324–329. doi:10.1001/archderm.1957.01550210048005
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