Structural studies on the extracellular acidic polysaccharide from Rhizobium trifolii 4S

Abstract The structure of an extracellular acidic polysaccharide produced by Rhizobium trifolii 4S was studied by fragmentation with phage-induced depolymerase, methylation analysis, digestion with exo-β- d -glycanases, and n.m.r. spectroscopy. The polysaccharide is composed of d -glucose, d -glucuronic acid, pyruvic acid, and acetic acid in the molar ratio of 5:2:1:2. The repeating unit is a heptasaccharide containing ( a ) terminal 4,6- O -(1-carboxyethylidene)- d -glucose (1 residue), ( b ) (1 → 3)-linked d -glucose (1 residue), ( c ) (1 → 4)-linked d -glucose (2 residues), ( d ) (1 → 4)-linked d -glucoronic acid (2 residues), and ( e ) (1 → 4), (1 → 6)-linked d -glucose (1 residue). A possible structure for the polysaccharide is proposed. The phage-induced depolymerase hydrolyzes linkages of 4- O -α- d -glucosyl-β- d -glucuronic acid adjacent to branching points.