Binding studies of a sialic acid-specific lectin from the horseshoe crab Carcinoscorpius rotunda cauda with various sialoglycoproteins.

Interaction of the sialic acid-specific lectin carcinoscorpin with various sialoglycoproteins was studied by using radioiodinated lectin. The binding of carcinoscorpin was dependent not only on sialic acid content but also on the type of glycosidic linkage and form (branched or linear) of the carbohydrate chains. Carcinoscorpin has different classes of binding sites, and binding follows a phenomenon of positive co-operativity. The effect of Ca2+ concentration on the binding was studied, and the optimal concentration was found to be 0.02 M. Effect of pH, temperature and other bivalent metal ions are also reported. From haemagglutination- and precipitation-inhibition studies, it was concluded that carcinoscorpin has multispecificity towards acidic sugars, and its relation to the biological role of the lectin in the horseshoe crab is discussed.