The presence of an endogenous lectin in early embryos ofXenopus laevis.

Xenopus laevis embryos were examined for the presence of endogenous carbohydrate binding proteins. Soluble extracts of cleavage, gastrula and neurula embryos are able to agglutinate trypsinized rabbit erythrocytes. Unlike other embryonic lectins this agglutination activity requires the presence of calcium ions but not of sulphydryl reducing agents. It is specifically inhibited by galactose and galactose containing derivatives. Thiodigalactoside is the most potent disaccharide inhibitor followed by lactose and melibiose respectively. Methyl α-D-galactopyranoside is a more effective inhibitor than its β anomer. N-acetyl-D-galactosamine, N-acetyl-D-glucosamine, methyl α-D-mannopyranoside andL-fucose do not inhibit activity at concentrations at or above 25 mM. EDTA and EGTA are also strong inhibitors of this activity. β-D-galactoside binding lectins present in the early chick embryo have been implicated in cell to cell and cell to substrate adhesiveness of extraembryonic chick endoderm cells. Since cells of the blastula inXenopus laevis possess surface receptors bearing terminal β-D-galactoside groups it is possible that this β-D-galactoside binding lectin may play a role in the control of cell surface mediated events during development.