Stabilization of solutions of feather keratins by sodium dodecyl sulphate

Feather keratins were extracted from chicken feathers with aqueous solutions of urea and 2-mercaptoethanol. After filtration of the insoluble residue, a feather keratin solution was obtained. Removal of 2-mercaptoethanol and urea by dialysis resulted in aggregation of the keratin polypeptide chains and oxidation of the cysteine residues to afford a gel. The addition of sodium dodecyl sulfate (SDS) to the keratin solution prior to dialysis prevented extensive aggregation of the keratin chains. The effect of the addition of various quantities of SDS on the rate of aggregation of the polypeptide chains and the rate of oxidation of cysteine residues during dialysis was studied. With size exclusion chromatography, it was found that lower initial SDS/keratin ratios (0.125–0.5 g SDS/g keratin) resulted in larger SDS–keratin complexes. This indicates that more intermolecular cross-links had formed. Higher SDS/keratin ratios (1–2 g SDS/g keratin) resulted in small SDS–keratin complexes, comparable in size to the keratin monomer. High amounts of SDS seemed to prevent the oxidation reaction between different keratin chains, resulting in more intramolecular disulfide bond formation.