Further characterization of the sialic acid-binding lectin from the horseshoe crab Carcinoscorpius rotunda cauda

A sialic acid-binding lectin, named carcinoscorpin, has been isolated from the horseshoe crab Carcinoscorpius rotunda cauda. It is a glycoprotein of molecular-weight 420,000, having two subunits of molecular weight 27,000 and 28,000, both subunits responding to glycoprotein stain. Leucine was detected as the only NH2-terminal amino acid. The sedimentation constant of the native lectin was found to be 12.7 s. On digestion with trypsin, the lectin gave 18 soluble tryptic peptides. This lectin was found to be antigenically unrelated to another sialic acid-binding lectin, limulin, isolated from the horseshoe crab Limulus polyphemus. A lectin-specific disaccharide alcohol namely O-(N-acetylneuraminyl) (2 → 6)2-acetamido-2-deoxy-D-galactitol was found to quench the typical tryptophan fluorescence of the native lectin at 332 nm. The association constant for this interaction was determined spectrofluorimetrically and found to be 1.82 × 103 M-1