Isolation and Partial Characterization of a Salt-extractable Globulin from Soybean Seeds

After exhaustive extraction of defatted soybean meals with water, the residues were extracted with a 0.5м NaCl solution. A globulin was isolated from the NaCl soluble fraction by ion-exchange chromatography on CM-Sepharose CL-6B. The isolated globulin, designated as basic 7S globulin, was homogeneous on gel electrophoresis, gel filtration and ultracentrifugation. This protein had higher isoelectric points at pH levels of 9.05 and 9.26 than did water-extractable globulins. SDS-gel electrophoresis of basic 7S globulin gave two kinds of subunits (Mr, 16000 and 26000) with the 2-mercaptoethanol (ME)-containing system and showed only one intermediate subunit (Mr, 42000) without ME. Therefore, two kinds of subunits were linked by disulfide bonds to form an intermediate subunit. The globulin molecule was found to be made up of four intermediate subunits which were determined by a cross-linking reagent followed by SDS-gel electrophoresis. The molecular weight was calculated to be 168000.