FURTHER CHARACTERIZATION OF THE SACCHARIDE SPECIFICITY OF SNAKE GOURD(TRICHOSANTHES ANGUINA) SEED LECTIN

The galactose-specific lectin present in the seeds of Trichosanthes an guina (snake gourd) has been further characterized by isoelectrofocusi ng experiments to identify the number of isolectins. Its carbohydrate- binding specificity has also been characterized in greater detail by t he haemagglutination-inhibition technique using several mono-, di- and oligosaccharides. The results suggest that affinity purified snake go urd seed lectin (SGSL) is made up of a single isolectin with a pi of 5 .0. The lectin exhibits a strong preference for the beta-anomer of gal actose over the alpha-anomer and ligands with a hydrophobic moiety att ached to the beta-anomer of galactose such as p-nitrophenyl-beta-D-gal actopyranoside and 4-methyl-umbelliferyl-beta-D-galactopyranoside, inh ibit the lectin activity better than the simple methyl glycosides of g alactose, suggesting that additional hydrophobic interactions stabiliz e the binding of these ligands bearing nonpolar moieties. The disaccha rides lactulose and thiodigalactoside exhibit considerably higher affi nity than lactose and Me beta GaI, indicating that their reducing suga r moieties may have additional favourable interactions with the lectin combining site.