The Preparation and Properties of a Helix-rich Fraction Obtained by Partial Proteolysis of Low Sulfur S-Carboxymethylkerateine from Wool

Abstract

Abstract 1. The low sulfur fraction of S-carboxymethyl wool keratin, which has an α-helix content of about 50% in aqueous solution, has been subjected to partial proteolysis with the enzyme Pronase P to yield an acid-precipitable fraction with a helix content of about 85%. 2. The optimum conditions for the preparation of this fraction have been studied with respect to time, temperature, pH, enzyme concentration, and Ca++ concentration. 3. In dilute solution the material appears to consist chiefly of particles with a molecular weight of about 41,000 and an axial ratio of 8:1 to 10:1. The dimensions are consistent with a multistranded, rod-like particle made up of probably three α-helical chains. 4. In 8 m urea, the particles break down irreversibly to a heterogeneous mixture, with molecular weights in the range 2000 to 5000, which suggests that peptide bonds are broken in the helical segment during proteolysis, but the integrity of the particle is maintained by its multistranded structure. Both gel chromatography and gel electrophoresis indicate that the helix-rich particle is derived from the major helical components of the low sulfur fraction of S-carboxymethyl wool keratin. 5. Amino acid analysis of the helix-rich fraction shows that, compared to the low sulfur fraction of S-carboxymethyl wool keratin, it is enriched in the helix-favoring residues lysine, leucine, alanine, and glutamic and aspartic acids and depleted in the helix-inhibiting residues S-carboxymethylcysteine, proline, serine, threonine, and glycine.