Concanavalin biological activities

To immobilize a protein the biologic activity of which depends on a cofactor, this cofactor has to be present in sufficient concentration during the immobilization step. Thus, for example, the lectin Concanavalin A is immobilized in the presence of a buffer containing 0.1 M glucose or a-methylmannoside, 1 mM calcium chloride and 1 mM manganese chloride. 

It is generally assumed that Ca2+ sites cannot be designed to exclude Ln3+ ions. There are a number of exceptions to this generality. Some examples are Ln3+ ions cannot replace Ca2+ in scallop myosin [4], concanavalin A [5] Ca2+ ions cannot displace Gd3+ from IgG [6]. Sometimes the reduced oxidation state of the Ln ion is useful. An example of this is the binding of Eu2+ to concanavalin A and restore biological activity to the apoprotein [7]. 

Antibodies specific for the active site of concanavalin A have been isolated from rabbit sera. Two antibody fractions, which were isolated after affinity chromatographic separation on immobilized concanavalin A, showed distinct differences in biological activity. One population of antibodies was directed to the active site of the lectin, and binding of the antibody in this case is inhibited by methyl cv-D-mannopyranoside, whereas the other antibodies were directed to the antigenic determinants on the concanavalin A molecule. 

Concanavalin A, a protein (isolated from jack-beans) which binds carbohydrates and has the general properties of a lectin , agglutinates and inhibits growth of malignant cells (Sharon and Lis, 1972), but it also agglutinates erythrocytes. Each monomeric unit of concanavalin A has one site that binds calcium ions and another that binds Zn ", Co ", or Mn-" ", and both sites must be occupied by the appropriate metal for biological activity to occur. 

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