Immunochemical studies on the capsular polysaccharide of pneumococcal type IX.

1. In addition to the previously identified components, d-glucose, N-acetyl-d-glucosamine and d-glucuronic acid, the immunologically specific capsular polysaccharide of pneumococcal type IX (polysaccharide S IX) is now found to contain mannosamine and galactosamine, probably as their N-acetyl derivatives. 2. Partial hydrolysis yields a complex mixture of oligosaccharides, several of which have been separated. 3. One of these is alpha-d-glucuronopyranosyl-(1-->3)-d-glucose. It is an inhibitor of the precipitation of antipneumococcal type IX serum by polysaccharide S IX. 4. Two others, d-glucuronopyranosyl-(1-->3)-d-glucosamine and d-glucuronopyranosyl-(1-->3)-d-galactosamine have been identified and a trisaccharide and pentasaccharide partially characterized.