Effect of sodium dodecyl sulphate on the 12S fraction of mustard proteins (B. juncea).

The effect of SDS on the 12S protein fraction of mustard seed (B. juncea) has been followed by the techniques of ultracentrifugation, gel filtration, gel electrophoresis, viscosity, ultraviolet difference spectra and fluorescence spectra. At low concentrations of SDS, up to 0.1%, both aggregation and dissociation of the protein occurs. Only dissociation occurs at higher SDS concentrations and is complete at 0.5% SDS. Viscosity increases sharply up to 0.15% SDS, remains constant between 0.15 and 0.30% and then increases markedly again. SDS induces also difference spectra with minima at 280, 288 and 295 nm. Fluorescence emission intensity increases at SDS concentrations less than 0.05% and quenching occurs at higher SDS concentrations. The results suggest that SDS causes association, dissociation and denaturation of the protein molecule.