The electrophoretic behavior of a soy protein isolate was analyzed in both nonreducing and reducing
SDS-PAGE. Aggregates formed by a and a’ subunits of P-conglycinin exhibited both ionic
interactions and disulfide bonds. Higher molecular weight aggregates (180 000-190 000) consisted
of trimers or dimers of a’ and a subunits, whereas those of intermediate molecular weight (115 000-
120 000) were formed by a’,a subunits of P-conglycinin and A polypeptides of glycinin. The latter
exhibited a higher sensitivity toward changes of ionic strength and thermal treatments. The
proportion of a’ and a subunits of the isolate which was included in these aggregates is highly
dependant on the freeze-drying conditions. These aggregates were readily reduced in the presence
of NazS03, even at low concentrations and in the absence of denaturing agents, thus suggesting
that the disulfide bonds involved were accessible. These aggregates were stable at different pH
values, in the presence of both SDS and urea.