EXOCELLULAR BACTERIAL POLYSACCHARIDE FROM XANTHOMONAS CAMPESTRIS NRRL B-1459: PART III. STRUCTURE

Abstract

Periodate oxidation showed that the O-acetyl groups in the polysaccharide sterically affected the rate but not the extent of oxidation of the D-mannose residues, two-thirds of which were glycosidically substituted at C2by a D-glucuronic acid residue and one-third of which was linked as a terminal side-chain residue. The D-glucose and D-glucuronic acid residues oxidized by periodate were substituted at C4, but both were more resistant to oxidation than were the D-mannose residues. One-third of the D-glucose residues and a significant quantity of the D-glucuronic acid residues were inert to vigorous periodate oxidation and may bear side-chain residues. Quantitative recovery of the periodate-stable D-glucose residues as 2-O-β-D-glucopyranosyl-D-erythritol, after the oxidized polysaccharide was reduced with sodium borohydride and hydrolyzed with mild acid, revealed that two-thirds of the D-glucose residues were in pairs linked (β, 1 → 4). The pyruvic acid linkage in the polysaccharide was established as a 4,6-O-1-carboxyethylidene ketal attached to a terminal D-glucose side-chain residue. The structure of the polysaccharide is discussed in relation to its anomalous viscosity behavior in salt solutions.