Interactions of Saccharides with Concanavalin A

Previous studies (Kalb, A. J., and Levitzki, A. (1968) Biochem. J. 109, 669; Shoham, M., Kalb, A.J., and Pecht, I. (1973) Biochemistry 12, 1914) were interpreted as showing that transition metal and calcium ions must be bound to concanavalin A before this lectin can bind sugars. In contrast, we find that the addition of calcium ions fails to affect the following properties of manganese concanavalin A if the metalloprotein is prepared in their presence: (a) ESR spectrum of the manganese ion in the protein; (b) spin-lattice relaxation time of solvent water protons measured in the presence of the protein; and (c) 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 as observed by Barber and Carver (Barber, B. H., and Carver, J. P. (1973) J. Biol. Chem. 248, 3353).