The role of histidine in human epidermis

Incorporation of radioactively-labelled histidine into half-thickness skin and into the major protein fraction extracted from epidermis by urea (protein Fraction A) has been measured and compared with the amount of labelled urocanic acid appearing in the same specimen. After a short lag period, incorporation into half-thickness skin and into protein Fraction A was found to be linear up to 23 h of the study. Histidine appeared to be initially preferentially deaminated to urocanic acid. The somewhat erratic presence of urocanic acid at later periods is attributed to its high instability and solubility.