Quantitative precipitin studies on the specificity of an extract from Tridacna maxima (Röding).

Haemolymph from the clam Tridacna maxima precipitated with purified H-blood-group substances, Helix pomatia galactogen, and pneumococcus type XIV polysaccharide. Although gel diffusion, gel electrophoresis, and inhibition experiments indicated that only a single precipitating lectin was present in the haemolymph, quantitative precipitin and haemagglutination results suggested that a second agglutinin with anti-H-like specificity was also present. Evidence obtained from hapten inhibition experiments indicated that the precipitin that reacts with pneumococcus type XIV polysaccharide can be inhibited by a number of simple sugars. Of the compounds tested, 2-acetamido-2-deoxy-D-galactose was the best inhibitor of precipitation with pneumococcus type XIV polysaccharide and of haemagglutination with human erythrocytes, but the inhibition experiments showed that the extract was also markedly inhibited by D-galactosamine hydrochloride, D-galactose, lactose, and p-nitrophenyl beta-D-galactopyranoside. The latter compound was more active than its parent sugar, which was in turn a more potent inhibitor than p-nitrophenyl alpha-D-galactopyranoside. Melibiose, raffinose, and stachyose, compounds which each contain terminal alpha-linked D-galactopyranosyl residues, were relatively weak inhibitors. The combining sites of the lectin that reacts with pneumococcus type XIV polysaccharide appear, therefore, to be most complementary to 2-acetamido-2-deoxy-D-galactopyranosyl residues, probably in beta linkage.