CHEMICAL DIFFERENTIATION IN EPIDERMIS 593 ot/some type of inhibitor is indicated since extracts of epidermis depress the synthesis of protein by a cell-free preparation of rat liver (23). It is necessary to identify this inhibitor and eliminate it in order to obtain an adequate system in which epidermal protein synthesis--especially that of the HP--can be studied. Once this system is operative, it should be possible to test the RNA of the lower cells for "messenger" activity in order to determine whether failure to synthesize the HP in the lower cells is a result of a failure to transcribe the proper genome into messenger RNA. This type of investigation should provide information relevant to an understanding of control mechanisms of differentiation in the epidermis and other developing systems. ACKNOWLEDGMENT The author gratefully acknowledges the contributions to this investi- gation by those with whose names his is associated in the bibliography of this paper. (Received December 8, 1969) REFERENCES (1) Fukuyama, K., Nakamura, T., and Bernstein, I. A., Differentially localized incorporation of alnino acids in relation to epidermal keratinization in the newborn rat, Anat. Record, 152, 525-35 (1965). (2) Fukuyama, K., and Epstein, W. L., Epidermal keratinization: Localization of isotopically labeled amino acids, ]. Invest. Dermatol., 47, 551-9 (1966). (3) Fukuyama, K., and Bernstein, I. A., Autoradiographic studies of the incorporation of thymidine-aH into deoxyribonucleic acid in the skin of young rats, Ibid., 36, 321-6 (1961). (4) Fukuyama, K., and Epstein, W. L., Synthesis of RNA and protein during epidermal cell differentiation in man, Arch. Dermatol., 98, 75-9 (1968). (5) Fegeler, F., and Rahmann-Esser, M., Autoradiographische untersuchungen zum protein- und RNS- stoffwechsel der normalen menschlichen haut, Arch. Klin. Exptl. Dermatol., 228, 255-62 (1965). (6) Hoober, J. K., and Bernstein, I. A., Protein synthesis related to epidermal differentiation, Proc. Natl. Acad. $ci., US, 56, 594-601 (1966). (7) Fukuyama, K., and Bernstein, I. A., Site of synthesis of ribonucleic acid in mammalian epidermis, ]. Invest. Dermatol., 41, 47-52 (1963). (8) Gumucio, J., Feldkamp, C., and Bernstein, I. A., Studies of localization of "histidine- rich" peptide material in epidermis of the newborn rat, Ibid., 49, 545-51 (1967). (9) Fukuyama, K., and Epstein, W. L., Sulfur-containing proteins and epidermal keratiniza- tion, J. Cell. Biol., 40, 830-8 (1969). (10) Chakrabarti, S. G., and Bernstein, I. A., Sulh•r in epiderlnal chemical differentiation, Federation Proc., 26, 369 (1967). (11) Voorhees, J. J., Chakrabarti, S. G., and Bernstein, I. A., The metabolism of "histidine- rich" protein in normal and psoriatic keratinization, I. Invest. Dermatol., 51, 344-54 (1968).

594 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS (12) Chakrabarti, S. G., Sibrack, I,. A., and Bernstein, I. A., On the nature of the bond in epidermal protein cleaved by 0.1N perchloric acid (PCA) at 24øC, Abstracts, Meeting of the American Chemical Society, Atlantic City, September, 1968. (13) Sibrack, L. A., Chakrabarti, S. G., and Bernstein, I. A., The presence of "non-histidine" imidazole and copper in protein during epidermal differentiation, Abstracts, Meeting of the American Society for Cell Biology, Detroit, November, 1969. (14) Reaven, E. P., and Cox, A. J., Histidine and keratinization, J. Invest. Dermatol., 45, 422-31 (1965). (15) Baden, H. P., and Pathak, M. A., Urocanic acid in keratinizing tissue, Biochim. Biophys. Acta, 104, 200-4 (1965). (16) Tabachnik, J., Urocanic acid, the major acid soluble ultraviolet-absorbing compound in guinea pig epidermis, Arch. Biochem. Biophys., 70, 295-8 (1957). (17) Cox, A. J., and Reaven, E. P., Histidine and keratoh.yalin granules, ]. Invest. Dermatol., 49, 31-4 (1967). (18) Fukuyama, K., and Epstein, W. L., Ultrastructural autoradiographic studies of kcrato- hyalin granule formation, Ibid., 49, 595-604 (1967). (19) Feldkamp, C. S., Relation of the "histidine-rich" protein to keratohyalin, Thesis, The University of Michigan, Ann Arbor, 1969. (20) Ugel, A. R., Keratohyalin, extraction and in vitro aggregation, Science, 166, 250-1 (1969). (21) Chakrabarti, S. G., personal communication, 1969. (22) Sugawara, K., and Bernstein, I. A., Biosynthesis of epidermal "histidine-rich" protein in vitro, Abstracts, Meeting of the American Chemical Society, Chicago, September, 1967. (23) Freedberg, I. M., Fine, I. H., and Corddie, F. H.. Cell-free protein synthesis in mammal- Jan skin, ]. Invest. Dermatol., 48, 55-66 (1967).