DISSOCIATION, AGGREGATION AND DENATURATION OF SESAME α-GLOBULIN IN UREA AND GUANIDINE HYDROCHLORIDE SOLUTIONS*

Publisher Website
Google Scholar
Abstract
The effect of urea and GuHCl [guanidine hydrochloride] on the major protein of sesame seed (Sesamium indicum L.), .alpha.-globulin, was investigated by turbidity, sedimentation velocity, viscosity, difference spectra and fluorescence spectral measurements. The protein undergoes dissociation, aggregation and denaturation in the presence of the above denaturants. There is a critical concentration of denaturant where aggregation is maximum. Denaturation and aggregation are lower in buffers of high ionic strength. Dissociation and aggregation were explained by considering 2 types of subunits present in the protein molecule, 1 leading to a smaller sedimenting component and the other producing the aggregate. Amino acid analysis shows that the aggregated fraction is rich in aliphatic amino acid residues. The endothermic nature of the aggregation process was considered to arise from hydrophobic interaction of aliphatic side chains of the relevant subunits. The protein exists in a more denatured state in GuHCl than in urea solution.