STUDIES ON THE BIOCHEMISTRY OF EPIDERMIS .1. THE FREE AMINO ACIDS, AMMONIA, UROCANIC ACID AND NUCLEIC ACID CONTENT OF NORMAL ALBINO GUINEA PIG EPIDERMIS

[摘要] The epidermis of albino guinea pigs was analyzed and found to contain: ammonia, 0.40; urocanic acid (UCA), 0.53; total free amino acids, 11.0 (0.84 micromols/mg dry weight); RNA, 1.40; DNA, 1.24 and protein nitrogen, 11.8-calculated in per cent dry weight. The moisture content averages 64.4%. The concentration of total free amino acids in epidermis is about 3 times greater than that of guinea pig liver, kidney or spleen. Eighteen free amino acids were isolated from epidermis and determined quantitatively. The 5 amino acids found in highest concentration ( in per cent of the total amino acids) were serine, 20.2; glycine, 17.5; citrulline, 10.5; proline, 10.2; lysine, 10.0. Trace amounts of taurine and methionine were also present; other sulfur-containing amino acids were absent. Hydroxproline was present only in the bound form in epidermal collagen. There was 3.3% dry weight of this protein in epidermis, as contrasted with 73.0% in the dermis. By washing the epidermis repeatedly with isotonic sucrose, it was shown that about 85% of the total free amino acids, ammonia and UCA may be in the extracellular fluid and/or in the acellular stratum corneum. These results were compared with published data on the epidermis of other species, including human.