The Chemistry of Human Epidermis

Recently information has been presented concerning the close chemical relationship of the proteins of many ectodermal tissues. It has become increasingly clear that the keratins of these structures have a similar molecular pattern and may be tentatively defined as proteins which are resistant to digestion by pepsin and trypsin, which are insoluble in dilute acids, dilute alkalies, water, and inorganic solvents, and which on acid hydrolysis yield such quantities of histidine, lysine, and arginine that the approximate molecular ratios of these amino acids are respectively 1:4: 12 (Block and Vickery, 1931). It was significant that in these studies, which included among other keratins human hair and finger nails, no data concerning human epidermis were presented. Since histologically the nails and hair are considered as specialized and highly keratinized appendages of the epidermis, an analysis of this tissue might afford another chemical confirmation of the course of development. The material analyzed consisted of the layer of epidermis known as the stratum corneum. It was obtained from a patient having a subacute inflammatory condition of the skin diagnosed as dermatitis exfoliativa, a disease characterized by an abundant flaky desquamation of the upper two-thirds of the stratum corneum. Normally the cells of this area are dead, extremely desiccated, and partially keratinized but desquamation is so imperceptible as to make impossible the collection of a sample adequate for study.