Studies on the Carbohydrate Binding

The binding of carbohydrates to the hemelytic lectin CEL-III isolated from the marine inyertebrate dacumaria echinata was studied. Equilibrium dialysis data s"ggest that CEL-III has two carbohydrate-binding sites with equal aMnity. The binding of specific carbohydrates to CEL-III i"duces a decrease in the fluorescence intensity at 339 nm and the shift of the fluorescence emission maximum to a wavelength shorter by 3 nm, owing to the change in the enyironment of tryptophan. By ana]yzing the change in the fluorescence intensity at 339 nm as a function of the concentration of carbohydrates, the asseciation constants for binding of indiyidu al carbohydrates to CEL-III were calculated. The results indicate that GaiNAc, lactulose, and lactose are bound by CEL-III with fairly high alfinity among the carbohydrates tested. The pHdependence prefile of the association constant of lactose suggests that CEL-III binds carbohydrates with highest aMnity areund pH 5.0. Modification of CEL-III with IV:bromosllccinimide produces an oxidized deriyatiye, in which fQur tryptophan residueslmol were oxidized and had no hemolytic actiyity. However, two out of these four tryptophans escaped from the modification in the presence of specific saccharides and