A conformational change in concanavalin A detected by a calorimetric study of the binding of methyl α-D-mannopyranoside

The binding of methyl α-D-mannopyranoside to the lectin concanavalin A was studied by means of calorimetry. An apparent enthalpy of binding was also calculated from the variation of the equilibrium constant with temperature (van't Hoff ΔH). The ΔH measured directly was −30 to −38 kJ/mole indicating that the binding is driven by the ΔH change. In contrast, the van't Hoff ΔH was substantially smaller, about zero at pH 5.2. The difference in the ΔH measured directly and the van't Hoff ΔH implies that the conformation of concanavalin A undergoes a temperature dependent change at both pH's but most predominantly at pH 5.2. The existence of this conformational change was verified by difference absorption spectroscopy.