Assessment of Conformational Changes in Low-Sulphur S-Carboxymethylkerateine from Wool

Abstract

The effects of urea and guanidine hydrochloride on the ultraviolet absorption spectrum of the low-sulphur S-carboxymethylkerateine fraction of wool have been measured. In concentrated solutions of urea characteristic difference spectra were obtained with maxima of negative absorbance at 288, 280, and 240 miL. The addition of guanidine hydrochloride or an increase in temperature gave similar negative difference maxima at the higher wavelengths. Calculation of the extent of unfolding of the protein chains from the difference in absorbance at all three maxima showed that the unfolding was 50% complete at a urea concentration of about 1· 8M whereas a urea concep.tration of about 4· 3M was required to decrease the helix content by 50%. Similar measurements on components 7 and 8, the two major constituents of SCMKA, showed that a 50% decrease in helix content was obtained with 2·8M and O· 8M urea respectively whereas the corresponding values for 50 % unfolding assessed from difference spectral measurements were 2· 2M and 1· 2M urea respectively. It is suggested that the helical regions of components 7 and 8 aggregate specifically and that spectral measurements relate largely to non-helical portions of the chains.