Histidase activity of the skin in relation to the state of melanogenesis

The histidase reaction of the skin in relation to the state of melanogenesis was studied in animals (18 rabbits) and patients with vitiligo. The histidase activity and the content of urocanic acid were determined in skin biopsy material in order to study the reaction. The histidase activity of the skin of black rabbits was found to be twice as high as that of white rabbits. In the depigmented areas of the skin of patients with vitiligo the histidase reaction was depressed by comparison with areas of the skin with normal pigmentation in the same patients and with the skin of control persons. The dependence of the histidase reaction of the skin on the state of melanogenesis is dependent, it is suggested, on the inhibitory action of cysteine on the histidase and tyrosinase activity of the skin.