Interactions of saccharides with concanavalin A. Relation between calcium ions and the binding of saccharides to concanavalin A

Previous studies were interpreted as showing that transition metal and calcium ions must be bound to concanavalin A before this lectin can bind sugars. In contrast, it was found that the addition of calcium ions fails to affect the following properties of manganese concanavalin A if the metalloprotein is prepared in their presence: electron spin resonance spectrum of the manganese ion in the protein; spin lattice relaxation time of solvent water protons measured in the presence of the protein; and spin lattice and transverse relaxation times of the ¹³C carbons of α methyl D glucopyranoside (uniformly enriched with 14% ¹³C) in the presence of manganese concanavalin A. These results indicate that saccharide binding activity of the protein is independent of calcium ion binding if a transition metal ion (Mn²⁺) initially binds to the protein in the presence of calcium ions. The role of calcium ion binding to concanavalin A appears to be that of accelerating the rate of formation of the final transition metal protein complex.