Soluble wool Proteins. I. Light scattering and viscosity in Aqueous solution

Abstract

S-Carboxymethylkerateine 2 (SCMK2) and cc-keratose, two proteins derived from wool, have been characterized by nitrogen content, ultraviolet absorption, refractive index increment, light scattering, and intrinsic viscosity. Variations in the physical properties of different batches are attributed to different degrees of aggregation during the preparation. The relative viscosity decreased with time and was generally accompanied by an increase in turbidity, indicating aggregation. The effect of heating was to accelerate the fall in viscosity and increase in turbidity. Light scattering investigations showed that dissociation occurred on dilution and in some cases this could be detected by viscosity measurements. The molecular weight of several millions for SCMK2 at pH 6.7 was reduced to less than 1 million by removal of large aggregates by high-speed centrifuging, with an increase in both dissymmetry and intrinsic viscosity. In alkaline buffers at pH 10.5 the proteins were further dissociated and gave molecular weights of the order of 450,000. The behaviour of α-keratose was similar to that of SCMK2. Measurements on SCNK2 carried out in the presence of sodium dodecyl sulphate gave a molecular weight of 142,000 for the detergent-protein complex, corresponding to 95,000 for the protein, the dissymmetry was near unity and the intrinsic viscosity 0.11₅ dl/g. In 10M acetic acid, 8M urea, and 641 guanidine hydrochloride the apparent molecular weights were 95,000, 140,000, and 210,000 respectively, but these values are only upper limits because of possible selective solvation of the solvent component in such three-component systems.