Structure of l-arabino- d-galactan-containing glycoproteins from radish leaves

Abstract

Two l-arabino- d-galactan-containing glycoproteins having a potent inhibitory activity against eel anti-H agglutinin were isolated from the hot saline extracts of mature radish leaves and characterized to have a similar monosaccharide composition that consists of l-arabinose, d-galactose, l-fucose, 4- O-methyl- d-glucuronic acid, and d-glucuronic acid residues. The chemical structure features of the carbohydrate components were investigated by carboxyl group reduction, methylation, periodate oxidation, partial acid hydrolysis, and digestion with exo- and endo-glycosidases, which indicated a backbone chain of (1→3)-linked β- d-galactosyl residues, to which side chains consisting of α-(1→6)-linked d-galactosyl residues were attached. The α- l-arabinofuranosyl residues were attached as single nonreducing groups and as O-2- or O-3-linked residues to O-3 of the β- d-galactosyl residues of the side chains. Single α- l-fucopyranosyl end groups were linked to O-2 of the l-arabinofuranosyl residues, and the 4- O-methyl-β- d-glucopyranosyluronic acid end groups were linked to d-galactosyl residues. The O-α- l-fucopyranosyl-(1→2)-α- l-arabinofuranosyl end-groups were shown to be responsible for the serological, H-like activity of the l-arabino- d-galactan glycoproteins. Reductive alkaline degradation of the glycoconjugates showed that a large proportion of the polysaccharide chains is conjugated with the polypeptide backbone through a 3- O- d-galactosylserine linkage.