Histidase function in human epidermal cells

The activity of histidase was studied in (1) epidermal tissue scraped from human infant foreskin, (2) fibroblast‐like cells in monolayer serial culture from human foreskin, and (3) epithelial‐like (epidermal) outgrowth from foreskin primary explants. Foreskin epidermal tissue without in vitro culture and epidermal outgrowth in primary culture from explants of foreskin showed equivalent mean levels of histidase activity, 5.22 × 10−3 and 5.01 × 10−3 μMoles urocanic acid produced per milligram protein per minute. Under the same assay conditions, there was no measurable histidase activity in cultured fibroblast‐like cells from foreskin at various times after subculture. The Km for enzyme from human foreskin epidermal tissue ranged between 2 and 5 × 10−3 M histidine. Ability to demonstrate the presence or absence of this tissue‐specific enzyme function in cultured cells suggests a useful means for studying differentiation, as well as a more precise way to identify epidermal origin of cultured cell types than morphological characteristics alone would permit.