Isolation and characterization of soluble beta-galactoside-binding lectins from mammalian liver

Soluble beta-galactoside-binding lectins were isolated by chromatography on asialofetuin-Sepharose-4B column in 10 mM Tris-HCl buffer (pH 7.5) containing 150 mM NaCl, 5 mM CaCl2 and 1 mM 2-mercaptoethanol. The three lectins moved essentially as single polypeptide bands, of 18, 22 and 24 kDa, respectively, for sheep, goat and buffalo hepatic lectins. Sheep and goat lectins each contained 4 mol of hexose, whereas the hexose content of the buffalo lectin was 7 mol. The number of sulfhydryl groups in sheep, goat and buffalo lectins were determined to be 3.2, 4.3 and 4.8, respectively. The optical properties of the three lectins were similar to those of tryptophan-containing proteins. Lectin-mediated hemagglutination of trypsinized rabbit erythrocytes was most effectively inhibited by lactose, followed by o-nitrophenyl beta-galactopyranoside and galactose, but remained unaffected by glucose, mannose, fucose and fructose. Calcium ions substantially enhanced their hemagglutinating activity. Goat and buffalo lectins, but not sheep lectin, were also stimulated by Mg2+, Mn2+, Sr2+ and Ni2+ ions. The lectins lost activity after treatment with para-hydroxy-mercuribenzoate and N-ethylmaleimide. However, iodoacetamide treatment had no effect on the activity. The results show that the three lectins are different from the soluble beta-galactoside-binding lectins studied thus far.