Crosslinking in keratins. III. Acid hydrolysis of keratins

Abstract

The fraction soluble during hydrolysis in an HCOOH–HCl–H2O mixture was measured as a function of time for Lincoln wool, human hair, and kid mohair. Evaluation by crosslinking theory of the equivalent relative increase in sulfur content of the three insoluble residues shows the likely presence of two components in each with equal sulfur content although the less abundant component differs by having mainly intramolecular crosslinking. Overall variation in sulfur content entirely accounts for the variation in rate of hydrolysis among these α-keratins. The data of Leach, Rogers, and Filshie for the amino acid content of the insoluble residue following hydrolysis of wool in dilute HCl also depend in a simple way on the amount dissolved; in this case the disproportionation of amino acids between the residue and extract depends on the degree of their affiliation with the crosslink-containing cystine.