Studies on the endogenous galactose-binding lectin during early development of the embryo of Xenopus laevis

Embryos of the frog Xenopus laevis at cleavage, blastula, gastrula and neurula stages contain a galactose-specific lectin. Extracts of gastrula embryos show the highest specific activity for this lectin compared to the other stages. Haemagglutinating activity of crude extracts is inhibited by lactose, alpha-galactose, beta-galactose, alpha Gal(1----4) beta Gal, beta Gal(1----3) alpha GalNAc, beta Gal(1----3) beta GlcNAc, beta Gal (1----4) beta GlcNAc, and most effectively by the disaccharide alpha Gal(1----3) beta Gal. Lectin from all stages was purified by absorption to galactose-linked immunoadsorbent or by affinity chromatography on a column of p-aminophenyl-beta-D-lactoside coupled to Sepharose 4B. In order to identify a single lectin band under reducing conditions in sodium dodecyl sulphate/polyacrylamide electrophoresis SDS/PAGE, it was necessary to treat aqueous suspensions of the purified lectin with chloroform/methanol (2:1, v/v). The lectin remained in the aqueous layer and gave rise on SDS/PAGE to a distinct band of 65 500 +/- 2780 molecular weight. Aqueous suspensions of the purified lectin that were not subjected to extraction with chloroform/methanol gave rise to several bands. Isoelectric focussing of the purified lectin resulted in two bands that separated at pI 4.3 and 4.5. In aqueous solution in the presence of lactose the chloroform/methanol-treated lectin appears to be an aggregate of apparent molecular weight of 375 000; the non-treated lectin under the same conditions has an apparent molecular weight of 490 000.