Purification and Characterization of a Lectin from Rice Bran

A rice bran lectin was purified to homogeneity by precipitation with ammonium sulfate and chromatography on ovomucoid-Sepharose and CM-cellulose. The molecular weight of the dimer lectin was estimated to be around 37,000 by ultracentrifugation studies. The sedimentation coefficient was 3.8S. On Sepharose 6B gel filtration in the presence of 6 M guanidine-HCl, the lectin showed a molecular weight of 19,000. On reduction and carboxymethylation, the lectin further dissociated into two nonidentical subunits, with molecular weights of about 11,000 and 8,000. These subunits did not show hemagglutinating activity. Equilibrium dialysis experiments using N-acetyl-[1-14C]glucosamine indicated that about 1.8 mol of the sugar was bound to 19,000 g of the lectin. The lectin was mitogenic against mouse splenic lymphocytes and human peripheral lymphocytes. The lectin enhanced the rate of glucose oxidation and inhibited epinephrine-stimulated lipolysis in mouse adipocytes. Some characteristics of the lectin are compared with those of wheat germ agglutinin.