Soybean Basic 7S Globulin which was Detected from Okara and its Isolation Methods

Abstract

Basic 7S globulin, an unique protein in soybean seed proteins, was detected in the residue of soymilk production (Okara). A new preparation method of the protein from Okara was studied. Though the basic 7S globulin was not extracted with water, the protein was extracted with 0.3M NaCl, denaturant (6M urea or 0.1% sodium dodecyl sulfate) or a high pH solution, indicating that the protein associated with Okara through non-covalent bonds. On the other hand, the basic 7S globulin was not extracted even with the denaturants at 60°C or above. The two subunit bands (HMWS and LMWS) of the basic 7S globulin were observed in an extract with the denaturant containing 2-mercaptoethanol at 0.02M or above even in this high temperature. After heating with a solution containing N-ethylmaleimide, an intermidiata subunit band (IS) of the protein was detected. These results indicated that the protein easily made crosslinks through disulfide bridge upon heating. The basic 7S globulin extracted from Okara was purified on CM-Sepharose CL-6B. Two fraction (F1 and F2) obtained were 85kDa and 42kDa by HPLC. The electrophoretic patterns of the fraction, however, showed the same on SDS-urea electrophoresis, which suggested that the F1 fraction contained the dimer and the F2 fraction contained the monomer of the protein. The yield was 2.2% of soybean seeds. This preparation method was better than the previous methods on the yield and reproducibility.