METAL ION REQUIREMENTS OF CONCANAVALIN A.

Concanavalin A, the lectin or plant hemagglutinin obtained from Canavalia ensiformis, contains the metals manganese and calcium in its native state. Several workers have shown that the protein has two transition metal binding sites (S1) and two calcium ion binding sites (S2) per dimer of molecular weight 53,000 (1-3). The protein must have a full complement of these metal ions for optimal binding of saccharides. Earlier, water proton relaxation rate and fluorescence titrations gave evidence of two strong and two weak lanthanide binding sites per dimer of apo-concanavalin A. These studies suggested that the lanthanide ions not only substitute for calcium in S2 but also bind at S1 with an association constant similar to that of manganese. The paper reports the effects of the substitution of these ions upon the proteins' ability to bind saccharides.