The binding of dyes by soluble wool keratin derivatives

Abstract

The binding of three acid dyes of slightly differing composition to a soluble wool keratin derivative has been measured by the dialysis-equilibrium method. The data satisfy the Klotz-Scatchard equation for the binding of small ions to proteins but the maximum amount of dye bound is much less than that equivalent to the number of basic side chains on the protein, given by amino acid analysis. It seems likely that the guanidino groups of the arginine residues are not able to bind dye anions, and it is suggested that this occurs because they are more firmly bound to other groups on the protein. Intermolecular bonding of this type would account for the high degree of aggregation shown by the soluble wool protein. The influence of pH and ionic strength on the binding of the three dyes is discussed in relation to their chemical structure.