Amino Acids in Human Skin. ∗

Abstract

The outer layers of human skin were successively extracted in the cold with 95% alcohol, ethyl ether and chloroform. The material was then digested with commercial pepsin for 72 hours and for a similar length of time with commercial trypsin. The residual dry product contained 6.1% of ash and 14.2% of total nitrogen. Some of it was analyzed by means of the Van Slyke partition method. Cystine was determined according to Folin and Marenzi and tyrosine and tryptophane by the Folin and Ciocalteu procedure. The values for the basic amino acids (Van Slyke method) were recalculated and are shown in the table in terms of per cent in the residual skin. This was done in order that a comparison could be made with the results obtained by Wilkerson, 1 who recently reported on the chemical nature of human skin. Wilkerson used a modification of the Vickery and Leavenworth method for the basic amino acids, but the remainder of his data were obtained by the same procedures employed by the writer. The values shown in Table I are those obtained by the writer as well as those published by Wilkerson. Those given for human nitrogen and amide nitrogen are expressed in terms of total nitrogen while the ones shown for the amino acids are given in terms of the residual tissue. It is clear from the tabulations that a considerable difference exists between the two sets of data. This may be due to the fact that whereas the author analyzed skin that had been digested with proteolytic enzymes, Wilkerson merely examined partially defatted skin. On the other hand, Block 2 who digested skin with pepsin found 6.0% of arginine, 4.5% of lysine, and 0.82% of histidine in his dry digested material. Block's results are in accordance with the writer's. Block also used a modification of the Vickery and Leavenworth method.