Calorimetric study of the binding reaction of concanavalin A with immunoglublins

The thermal effects associated with the binding reaction of concanavalin A and immunoglobulins have been measured by calorimetry. IgG solutions do not generate heat on mixing with concanavalin A, confirming the low reactivity of IgG for the lectin molecule. IgM solutions, on the other hand, show a substantial enthalpic contribution of delta H = -24 +/- 1kJ/site for the binding reaction between the polysaccharide chains of human IgM macroglobulin and concanavalin. A stoichiometry is 10 monovalent concanavalin A molecules per intact macroglobulin and two bivalent concanavalin A molecules per two sites on the heavy chain of the reduced macroglobulin subunit.