Structural studies on the lipopolysaccharide of a rough strain of Escherichia coli

The determination of the 2-keto-3-deoxyoctonic acid (KDO) content of a lipopolysaccharide obtained from Escherichia coli ATCC 12408 using the thiobarbituric acid and semicarbazide methods for its estimation points to the presence of a KDO trisaccharide unit in the structure. On partial hydrolysis of the lipopolysaccharide by the method of Painter, using polystyrene sulphonic acid, up to 60% of the KDO was lost. A core oligosaccharide, with a molecular weight in the region of 3500 to 5000 and containing heptose, glucose, galactose, KDO and phosphorus in the molar ratio of 2:1.44:0.6:0.3:1.3, was isolated on fractionation of the dialysate on Sephadex G-15. Sodium borohydride reduction of the oligosaccharide results in the loss of both reducing power and KDO, indicating a linear-type structure with KDO only at the reducing end. Removal of phosphate from the oligosaccharide had no significant effect on its molecular weight. Periodate oxidation, followed by borohydride reduction, and methylation studies showed the presence of certain structural features similar to those already found for the core region of lipopolysaccharides from other gram-negative bacteria.