Determination of Glycinin and ß-Conglycinin in Soybean Proteins by Immunological Methods Setsuko Iwabuchi* and Fumio Yamauchi Glycinin and /3-conglycinin contents in soybean seeds and in protein fractions were immunologically assayed. Whole extractable proteins (WBE) were composed of 32% glycinin, 23% /3-conglycinin, and 45% remainder unassayed by anti-glycinin and anti-/3-conglycinin. The acid-precipitable fraction (APP) at pH 4.8 was composed of 34% glycinin, 27% /3-conglycinin, and 39% remainder. The protein composition of APP was similar to that of WBE. The crude 7S, precipitating at pH 4.8, was composed of 52% /3-conglycinin, 3% glycinin, and 45% remainder. However, the remainder content in the pH 6.4 precipitated fraction (crude 11S) was reduced from 45% to 15%. Thus, the amount of contaminating protein in globulin fraction is proportional to the acidity. Treatment with 10% NaCl and ammonium sulfate fractionation improved the glycinin plus /3-conglycinin content. Contaminating proteins were evidently concentrated in a 0-51% saturated ammonium sulfate precipitated fraction.

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A heat-induced transparent solution consisting of dissociates can be prepared under appropriate conditions: 8-conglycinin preparations, pH, and salt affected the thermal dissociation. Experimental conditions studying quantitative dissociation into subunits and analyzing the dissociation process using gel filtration without artifact are examined. P-Conglycinin dissolved in distilled water (0.5 ?6 w/v, pH 7.5) can be heated without turbidity even at 100 "C for 30 min. The elution buffer, 3.2 mM potassium phosphate (pH 7.6, Z = 0.01), did not affect the gel filtration profile of heat-induced products, whereas buffers of ionic strength above 0.02 caused aggregation of dissociate and a decrease in a portion of the dissociation peak. It was found that upon heating, P-conglycinin dissociated into its subunits and they can exist in dissociated form unless salt is added to the system. The main factor governing these dissociation characteristics of 8-conglycinin is considered to be that the mutual repulsion forces arising from hydrophilic domains of the subunits are superior to hydrophobic association.

The effects of heat and ionic strength upon dissociation or association of soybean proteins were characterized by an immunoelectrophoresis. Among thermal products of both glycinln and p-conglycinin, the dissociated subunits of p-conglycinin retained their antigenie reactivities, while the thermal products of glycinin lost their antigenic reactivities. Appearance of immunoprecipitin arcs was dependent on the ionic strength of the solutions. This is based on the conformational changes at the ionic strengths helow 0.1 where the thermal denaturation of p-conglycinin transforms from association to dissociation. The immunoelectrophoretic results can be used to determine the ionic strength of the solution in complex systems including whole soybean extracts and soybean milk. Relationship between the differences in textural properties of tofu and conformational changes of soybean protein is discussed.