Structural Studies on O-Specific Polysaccharide of Shigella flexneri Serotype 6

O-specific chain of Shigella flexneri 6 lipopolysaccharide was found to be composed mainly of rhamnose, N-acetylgalactosamine and O-acetyl groups in molar ratio 2.2 : 1.0 : 0.64, respectively. The presence of N-acetylgalactosamine, a distinguished feature of the lipopolysaccharide from serotype 6 was proved by several methods. The following tentative structure for the repeating unit of Sh. flexneri 6 O-specific chain has been proposed: From the serological studies it could be concluded that β-l-rhamnosyl-1,3-N-acetyl-d-galactosaminyl sequence is involved in the type VI specificity, but the presence of O-acetyl and N-acetyl groups is not a necessary condition for it.