Mammalian epidermal keratin: isolation and characterization of the alpha-helical proteins from newborn rat

Neutral buffer-insoluble proteins extracted from newborn rat epidermis with alkaline urea have been purified by chromatography on Sephadex G-150 columns run in the presence of sodium dodecyl sulfate. Two proteins with apparent molecular weights of 60 000 and 68 000, respectively have been isolated and characterized. Spectropolarimetric studies show both of them to be alpha-helical in contrast to the non-helical heavier and lighter species also solubilized with alkaline urea. The amino acid composition of the two proteins, their electrophoretic behavior and their immunological characteristics are essentially identical. Both proteins appear to be major constituents of rat epidermal tonofilaments.