Biochemical Characterization of Soybean Protein Consisting of Different Subunits of Glycinin

Abstract

Soybean isogenic lines having different glycinin subunit compositions are now being bred. To compare the characteristics of the genetically improved soybean proteins, total protein and purified glycinin proteins were investigated in this study. The absence of subunit(s) resulted in marked changes in the proportion of glycinin to β-conglycinin. When the pH of the total protein and glycinin solution was changed and NaCl was added to the solution, glycinin consisting of only group I subunits and β-conglycinin are highly soluble compared to the A₅A₄B₃ or A₃B₄ subunit at a NaCl concentration lower than 0.05 M at pH 5.5. Ultracentrifuge analysis showed that the glycinin containing all subunits was able to assemble to form the 11S structure. That consisting of group I subunits formed a uniform 7S structure. Decreasing glycinin/β-conglycinin ratios and structural changes caused by a lack of glycinin subunit(s) are thus expected to influence the food-processing properties of soybeans. Keywords: Soybean; glycinin; mutant; subunit composition