Binding of manno-oligosaccharides to concanavalin A. Substitution titration with a fluorescent-indicator ligand.

The association constants for binding of methyl alpha-D-mannopyranoside (I), mannobiose (II) and mannotriose (III) to concanavalin A were determined in the temperature range 285-313 K by a substitution titration, using 4-methylumbelliferyl alpha-D-mannopyranoside as a carbohydrate-specific and fluorescent indicator. All binding equilibria are simple, but establish extremely slowly with II and III. At 298.3 K, K increases moderately from I to III: (6.4 +/- 0.5) x 10(3), (1.2 +/- 0.1) x 10(4) and (1.10 +/- 0.05) x 10(5) M-1. For binding of I, II and III, the - delta H degree values are constant (36 +/- 2 kJ mol-1) and equal to the average value (36.1 +/- 0.6 kJ mol-1) obtained for the three corresponding 4-methylumbelliferyl alpha-D-manno-oligosaccharides [Van Landschoot, A., Loontiens, F. G., and De Bruyne, C. K (1978) Eur. J. Biochem. 83, 277-285]. The data are interpreted as arising from specific binding to a single mannopyranosyl residue in (alpha 1 leads to 2)-linked manno-oligosaccharides.