Purification and characterization of a lectin from the shellfish, Saxidomus purpuratus

A lectin was purified from a shellfish, Saxidomus purpuratus, using ion-exchange chromatography on DEAE-cellulose and affinity chromatography on N-acetylglucosamine-Sepharose. The lectin purified by affinity chromatography showed seven protein bands in polyacrylamide gel electrophoresis. The two major lectins (SPA-I and SPA-III) were purified by a second DEAE-cellulose column chromatography. The molecular weights of the lectins were almost the same and were estimated to be around 40,000 by gel filtration on a Sepharose 6B column. On SDS-polyacrylamide gel electrophoresis in the presence of 2-mercaptoethanol, the lectins showed molecular weights of 14,000. The isoelectric points of SPA-I and -III were estimated to be 4.4 and 4.1, respectively. The two lectins (SPA-I and -III) differed slightly in amino acid composition and were glycoproteins containing 2.1 and 3.8 mol of GlcNAc per 40,000 g of the lectin, respectively. The binding constant of SPA-I or SPA-III for methyl N-acetyl-a-D-glucosamide, the strongest inhibitor of hemagglutination in this experiment, was estimated to be 1.3 X 10(3) or 4.2 X 10(4) M-1, respectively, by the UV difference spectroscopy method.