Cadmium-Binding Capacity of a Soybean Protein Fraction

Abstract

The cadmium-binding capacity of the soybean protein fraction was determined by equilibrium dialysis. The aqueous supernatant was extracted from the soybeans with 0.01M Tris-hydrochloric acid buffer (pH 7.4) by ultracentrifugation. The protein fraction (F-I, >10, 000 in molecular weight) was separated from the extract by Sephadex G-50 chromatography. Binding measurement was carried out in 0.01M Tris-hydrochloric acid buffer (pH 7.4). The binding data were analyzed according to the Scatchard equation. A Scatchard plot of the binding data showed several phases, indicating heterogeneity of the binding sites. The maximum amount of cadmium bound by F-I was calculated to be 43, 000μg/g. When cadmium was added to the aqueous supernatant, five cadmium-binding fractions (at molecular weights of>100, 000, 75, 000, 38, 000, and two low-molecular species) were detected by chromatography on Sephadex G-100. The major cadmium-binding fraction in F-I was the macromolecular species of>100, 000 in molecular weight.