Molecular size, shape and aggregation of soluble feather keratin

Abstract

Solutions of feather keratin were prepared by dispersion in urea and bisulfite and by oxidation with performic acid. The cysteine-cystine ratio of keratin thus dissolved depends on urea concentration and pH. The physical properties of the solutions were measured and correlated with the cystine and cysteine contents. Measurements of osmotic pressure, turbidity, sedimentation rate and viscosity indicated that in infinitely dilute solution keratin has a molecular weight of 10,000 and an axial ratio of 13. Preparations which contain both free[long dash]SH groups and[long dash]S[long dash]S[long dash]bonds associate with increasing concentration. The association involved formation of intermolecular[long dash]S[long dash]S[long dash]bonds at the expense of intramolecular bonds. Association produced a particle which was more asymmetric than the monomer. Keratin sedimented with a single boundary in the ultracentrifuge. The variation of the viscosity, osmotic pressure, sedimentation rate and turbidity with concentration of dissolved keratin is discussed.