Modification of human prekeratin during epidermal differentiation.

The polypeptide-chain components of human epidermal prekeratin and keratin were analysed by high-resolution SDS (sodium dodecyl sulphate)/polyacrylamide-gradient-gel electrophoresis. Size heterogeneity existed amongst prekeratin components and at least ten polypeptides, in the molecular-weight range 46,000-70,000, were observed in 0.1 M-citric acid/sodium citrate buffer (pH 2.65) extracts of scale epidermis. Prekeratin from scalp pilosebaceous ducts was identical with that from the contiguous epidermis, and no prekeratin was found in extracts of scale dermis. Prekeratin from plantar epidermis contained additional polypeptide chains, but only slight anatomical variation existed between the non-callus sites examined. Keratin differed from prekeratin in at least two major respects: (a) many major components did not co-electrophorese on high-resolution SDS/polyacrylamide slab gels, and (b) keratin, but not prekeratin, required denaturing and reducing conditions for extraction. Keratin extracted from scale epidermis after complete removal of prekeratin was identical with forearm stratum-corneum keratin. Palmar and plantar keratin contained additional polypeptide chains and had a different size distribution compared with forearm and scalp keratin components. Modification of prekeratin components to produce the keratin polypeptide profile occurred during epidermal differentiation, and these changes appeared to take place in the granular-layer region of the epidermis.