PROTEINS OF MAMMALIAN EPIDERMIS

[摘要] Experimental evidence indicates that the structural proteins of epidermis are associated with the tonofibrils as the precursors of keratin. Tonofibrils may also play an important role in the adhesiveness of squamous cells. Information on the role of the fibrous protein in keratiniza-tion has largely accumulated from X-ray diffraction studies on epidermis and hair follicles. Bases on differences in chemical behavior of the pre-keratins of the hair follicle and results of X-ray diffraction studies, Mercer has formulated a theory of the process of keratinization. In the lower and intermediate layer of the malpighian stratum the molecules of the primary proteins of unknown shape or size may exist as organized particles of a corpuscular type protein. End to end linkage of the latter in the upper malpighian zone brings about the formation of a fibrous form of the protein. Since protein in fibrous form, in contrast to the hardened keratin, is digested with trypsin and 2 N HC1 and is converted into the disorganized beta form in water at 90-95[degree]C for 30 seconds, Mercer postulates that this fibrous form is held together by H bonds and salt linkages. The prekeratin zone is dissolved by a saturated urea solution, while in the area of keratinization this solution causes swelling, the degree of which decreases as the hardening becomes more complete. In the zone of keratinization formation of disulfide linkages between the protein chains occurs since a reversal of the solvent action of urea follows reduction of the -S-S bonds by Zn and HC1. Finally stabilization or formation of true keratin by cystine bridges appears to be brought about by the establishment of covalent links between the protein components in the direction of the fiber. Recent evidence indicates that keratin contains not only -S-S linkages but also sulfhydryl groups.....Importance of biochemical studies on the synthesis of keratin was discussed particularly since this process may be of great value for an understanding of the many diseases which afflict the skin and its appendages.