Partial Purification and Characterization of the 15S Globulin of Soybeans, a Dimer of Glycinin

During preparative gel filtration of crude glycinin (11S ultracentrifugal component of soybean proteins), the second fraction that eluted just before the major peak (glycinin) was found to be enriched in the 15S component. Gel electrophoresis under denaturing conditions indicated that this fraction was identical to glycinin, suggesting that the 15S component is an aggregate of glycinin. Upon rechromatography of pooled, freeze-dried, 15S-enriched (50% 15S prior to freeze-drying) fractions the purity of 15S was only 39%, apparently because of partial dissociation of the 15S fraction into 11S component as a result of dialysis and freeze-drying. When freeze-drying was avoided, two successive rechromatographies yielded 15S preparations of 63−66% purity. However, on storage in solution, the purified 15S fraction slowly dissociated into 11S component; after 20 days, the composition was 47% 15S and 31% 11S. Gel electrophoresis and amino acid analysis confirmed the identity of the 15S fraction with glycinin. Molec...