Cutaneous alkaline phosphatase: a biochemical study.

A fluorometric microassay of alkaline phosphatase is described; it is based on the hydrolysis of 4-methylumbelliferyl phosphate and is about three orders of magnitude more sensitive than the usual colorimetric procedures. When applied to skin, the addition of fluoride is necessary to avoid interference from the relatively high levels of acid phosphatase present in the epidermis. Kinetic data for cutaneous alkaline phosphatase are reported. Skin appears to contain a single enzyme of the 'bone-liver-kidney' type, which is present both in a soluble and in membrane-bound form. It occurs almost exclusively in the dermis, not more than 1% of the total alkaline phosphatase of human skin being present in the epidermis.