The polypeptide composition of epidermal prekeratin

An alpha-fibrous protein, prekeratin, has been isolated from cow snout epidermis with citrate buffer, pH 2.65. Using acrylamide electrophoresis with 0.1% sodium dodecyl sulfate, prekeratin can be shown to contain three polypeptide chains of different molecular weights. The two faster migrating components are very similar with a mol. wt of about 47,000 while the slower one has a mol. wt of about 58,000. Chromatography on a number of molecular sieve and exchange resins does not separate the components, but use of Sepharose 2B with 0.1 M Tris, pH 9.0, containing 10% propanol gives two peaks of protein. The first and major peak contains all three components while the second has only the two with the faster mobility. The two more rapidly migrating components and the slower one were isolated by acrylamide electrophoresis, and the latter has an amino acid composition more compatible with a non-helical protein. Enzymatic digestion with tosyl-L-phenylalanine chloromethylketone-treated (TPCK-)trypsin shows that the component of mol. wt 58,000 is more susceptible to hydrolysis than the other two. These data suggest that prekeratin is not homogenous in composition and consists of several interacting polypeptide chains. One of these components would appear to be non-helical in structure.