Effect of sulphydryl and disulphide compounds on the formation and quality of thermal aggregates of soya bean 11S globulin

The precipitate (thermal aggregates) formed in the presence of sulphydryl compounds > 0.01M [β-mercaptoethanol (ME), gutathione (reduced form) (GSH), and cysteine (oxidised form) (Cys)] consisted of a basic monomer subunit and oligomerised sub units but did not contain polymerised subunits. The content of the basic subunits in the precipitate increased with increasing concentrations of sulphydryl compounds, and on addition of 0.5M ME reached a level of 90% or more of the precipitate. The time course of the formation of the basic monomer subunit and oligomerised subunits showed that basic monomer subunits tended to be precipitated at the initial stages of heating. This was followed by the formation of oligomerised subunits. Heating an 11S globulin solution containing sulphydryl compounds accelerated the precipitation reaction. However, this did not produce a high degree of polymerisation due to sulphydryl-disulphide interchange. A scanning electronmicroscope image of thermal aggregation induced in the absence of any sulphydryl compounds showed, however, that polymerisation has a major role in the formation of a network structure. The mechanism of oligomer and polymer formation is discussed here.