Binding of methylumbelliferyl mannoside to concanavalin A under high pressure

The equilibrium binding of 4-methylumbelliferyl alpha-D-mannopyranoside to concanavalin A was measured by changes in fluorescence quenching observed at pressures ranging from 1 to 2000 bar (1974 atmospheres). From the pressure-induced changes in the apparent Ka, we calculated volume changes for the association reaction of -2.5 and -1.7 +/- 1 ml/mol for concanavalin A in its dimeric and tetrameric forms, respectively. This carbohydrate-binding reaction is less pressure-sensitive than other protein-ligand interactions that have been studied under pressure. The volume change observed is comparable to that expected for a reaction involving hydrogen bond formation, in a non-polar environment.