Studies on the Biochemistry of Epidermis IV. The Free Amino Acids, Ammonia, Urea, and Pyrrolidone Carboxylic Acid Contest of Conventional and Germ-Free Albino Guinea Pig Epidermis

The total free amino acids, ammonia, urea, and pyrrolidone carboxylic acid (PCA) were determined by ion exchange chromatography in conventional albino guinea pig epidermis, and their values were 305, 57.2, 37.7, and 270 μmoles/gm wet wt., respectively. Serine (25.1%) and glycine (15.6%) together comprised about 40% of the total free amino acids, and an additional 30% are equally divided between citrulline, alanine, and proline. Free cystine or cysteine was absent from epidermis but all of the remaining 19 free amino acids were about 200 fold higher in concentration in whole epidermis as compared with plasma. Germ-free epidermis had a higher taurine level than conventional epidermis, but all the other water-soluble nitrogen compounds were 2–4 fold greater in concentration in the latter tissue. The similarities far outweighed the differences between the free amino acid pattern (mole%) of conventional as compared to germ-free epidermis. The lower level of the nitrogen compounds in germ-free epidermis was attributed to an impairment of protein digestion in the gut due to a lack of microbial flora. Alterations in concentration of these compounds up to 6 days after 3000 rep β-irradiation of the skin were reported. The possible origin (s) and biological significance of these epidermal nitrogen compounds was discussed