Structural studies on the microfibrillar proteins of wool: characterization of the alpha-helix-rich particle produced by chymotryptic digestion.

The alpha-helix-rich particle produced by chymotryptic digestion of the reduced and alkylated microfibrillar proteins of wool was characterized by physicochemical methods. The preparations were homogeneous with respect to size and the particle molecular weight was found to be 50 200 +/- 2 000. Hydrodynamic methods indicated a length of about 20 nm for the particle. The properties of the particle, derived from two methods of isolation of the microfibrillar proteins, were identical and were also independent of the type of wool used. From a consideration of the molecular weight in denaturing solvents and from cross-linking experiments with dimethyl suberimidate a four-chain structure, consisting of a pair of double-stranded alpha-helices, is proposed for the particle.