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THE STRUCTURAL PROTEINS OF EPIDERMIS AND THEIR POSSIBLE RELATION TO AGING SKIN* By C. C^aaVT•IEaS, D. L. WOEa•rLE¾, A. B^VMLEa, and H. SHORTS Departments of Biochemistry and Biophysics, Roswell Park Memorial Institute, Buffalo 3, N.Y. EPIDERMIS OFFERS some unusual and interesting aspects of bio- chemical interest because this tissue is so different from any other tissue in the body. To quote Cowdry (1) "Epidermis is Nature's most effective frontier tissue. In it, life and death are more closely joined than anywhere else. The cells composing the tissue--all probably of one type, ecto- dermal-are well organized. They stand closely together. The inner cells, next to the underlying blood vessels of the dermis, have adequate supplies. Some of their descendents take up positions nearer and nearer to the external environment. The farther they move in this direction, the more unfavorable their living conditions become, not only as to supply, but also in respect to removal of waste. They gradually die, still more closely clasped together, and in such a condition that in death they serve as a protective shield of exceeding thinness, conditioned by the oily secretion of sebaceous glands." The primary function of epidermis, then, is to limit the organism and to protect other tissues from harmful changes in their environment. The structure of epidermis is such that the direct entry of water or its loss through this tissue is practically nil. Epidermis is repaired rapidly by cell multiplication and quick drying, and the necessity of this function is ap- parent from the fact that this tissue is subjected to such hazards as mechan- ical injury, extremes of heat and cold, radiation from the sun, micro6rgan- isms and ectodermal viruses. Perhaps the many external sources of irrita- tion to epidermis are responsible for the ease with which this tissue becomes hyperplastic and is thus highly susceptible to the induction of cancer. Epidermis offers to the biochemist an opportunity to study various phases of cellular growth (differentiation) concomitant with the biosyn- thesis of the complex fibrous protein, keratin. The wear and tear which * Presented at the May 13, 1955, Meeting, New York City. 324