Structural studies of capsular polysaccharide of type XII Diplococcus pneumoniae.

The capsular polysaccharide of Diplococctw pneumoniae Type XII contains residues of D-glucose and D-galactose in a molar ratio of 2:l. The methylated polysaccharide yielded upon hydrolysis 2,3,4,6-tetraand 3,4,6-tri-O-methyl-D-glucose and 2,3,4,6-tetra-0-methyl-D-galactose as the only neutral methyl sugars. Periodate oxidation of the polysaccharide resulted in destruction of all neutral sugars and immunochemical activity against rabbit antisera. Periodate oxidation of the methyl 0-methylglycosides obtained after hydrolysis of the methyiated polysaccharide indicated that at least 30% of the L-fucosamine residues are substituted at C-4 in the polysaccharide. It is concluded that the polysaccharide consists of a hexosamine backbone that is substituted by D-galactosyl and kojibiosyl side-chains. The proposed terminal D-galactosyl residues apparently are sterically hindered from interacting with several D-galactose-binding proteins.