Title: Keratin
Literature References: A protein obtained from hair, wool, horn, nails, claws, beaks, scales, membranes of egg shells and nerve tissue. There are two types of keratins-hard keratin of hair, horn, nails, etc., and soft keratin (pseudokeratin) of the epidermis, and whalebone: Rudall, Adv. Protein Chem. 7, 253-290 (1952). The keratins contain all of the common amino acids and differ from other fibrous structural proteins chiefly by their high cystine content. Sequence studies revealed no preferable grouping or periodicity. Amino acid compn of a few keratins: Tristram in H. Neurath, K. Bailey, The Proteins vol. 1A (Academic Press, New York, 1953) p 220. Stability of the protein is due to frequent primary valence cross-links (disulfide bonds) and secondary valence cross-links (hydrogen bonds) between neighboring polypeptide chains. Prepn of different forms for different purposes: Grassmann, DE 673203 and DE 682257 (both 1939). Molecular structure of a-keratin: Fraser et al., Nature 203, 1231 (1964); of b-keratin: M. L. Huggins, Macromolecules 13, 465 (1980). Reviews: Ward, Lundgren, Adv. Protein Chem. 9, 243-297 (1954); Crewther et al., ibid. 20, 191 (1965); Bradbury, ibid. 27, 111 (1973).
Properties: Characteristic properties ascribed to keratins: (a) insolubility in water, including aq solns of salts, hydrotropic substances, and dil acids and bases at temps not much above room temp; (b) resistance to proteolytic enzymes; (c) resistance to hydrolysis; (d) solvolysis by mixtures of substances which break the -S-S- bonds and the hydrogen bonds.
Use: Coating "enteric" pills which are unaffected in the stomach, but dissolved by the alkaline intestinal secretions. Detailed coating instructions: Dale, Pharm. J. 129, 494 (1932). Other uses are in formulations of foam type extinguishers and in the production of protein hydrolyzates.

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