| Abstract: | Binding of zinc by glycinin was determined in 0.5 M KCl at pH 6.2. The number of binding sites in the native protein was 51 for 8.5 μM glycinin. Protein modification studies identified the histidine residues as one of the binding sites, and comparison with published data on the histidine content of glycinin suggests that the majority of these residues are on the surface of the protein. Denaturation by 6 M urea increased the number of binding sites to 330. The number of zinc binding sites was found to vary with the protein concentration in 0.5 M KCl. The affinity of zinc for the protein varied with the protein concentration. Increasing the KCl concentration to 1.0 M decreased the affinity of zinc for the protein and increased the number of binding sites. Zinc preferentially binds to EDTA rather than to glycinin. Binding at pH 5.5 resulted in a reduction in the number of binding sites to 23. Ultracentrifugal analysis of glycinin in the presence and absence of zinc gave S20, W values of 13.1 and 11.1, respectively. Calcium and magnesium did not bind to glycinin in 0.5 M KCl at pH 6.2. |
