Interconversion between Monomer and Dimer of the 7S Globulin of Soybean Seed

Abstract

The 7S globulin of soybean seed was purified on concanavalin A-Sepharose 4B. It exists as monomers at a high ionic strength or at a low pH, whereas it associates to form dimers under the opposite conditions. The sedimentation coefficient of the monomer is 5.6S, and that of the dimer 10S, at a protein concentration of 0.16%. Since the interconversion between the monomer and the dimer proceeds fairly rapidly, the ultracentrifugal pattern of the mixture shows a single peak. The apparent sedimentation coefficient of the mixture successively changes between 5.6S and 10S, corresponding to the ratio of the amounts of the monomer and the dimer. The monomer reversibly dissociates into subunits with 5 m urea or 0.01 n HC1.