A Study on Keratin

Keratins are the proteins of epidermal and skeletal tissues which are insoluble in the usual protein solvents, not digested by trypsin or pepsin, and high in cystine content. Such a definition intentionally excludes fibroin, the major protein of silk. It will be shown in this paper that keratins can be converted into proteins soluble in alkali or acid, with a definite optimum pH of flocculation (which may be interpreted as an isoelectric point), and digestible by trypsin or pepsin. This is accomplished by breaking the disulfide bonds of the protein. Papers on the oxidation of keratins have been published by Lissizin (l), Stary (2), and WaldschmidtLeitz (3), who used bromine, permanganate, and HZOz as oxidants. Stary and Waldschmidt-Leitz have shown that the oxidized keratin is digested by trypsin. The oxidizing agents are not specific for the disulfide groups, but attack the protein molecule at other points, and they act very slowly. In contrast, the reductants will be shown to act very quickly and without bringing about any other appreciable chemical alteration than that concerned with the sulfur. These agents dissolve keratin only at alkaline reaction (pH 10 to 13), but the action is not due to alkali alone. Products prepared from the solutions behave as true proteins, and not as prod: ucts of hydrolysis. Their solutions are precipitated by ordinary protein precipitants such as sulfosalicylic acid and lose this property when digested by trypsin or pepsin. Reductants available for reduction of disulfide groups are thioglycolic acid, potassium cyanide, sodium sulfide, and sodium sulfite. The chemical process exhibited by these reagents on simple