Immunochemical determination of the configuration of a haptenic substituent

Quantitative inhibition of specific immune precipitation, a rapid microanalytical technique requiring no expensive equipment, was used to determine the stereoconfiguration of pyruvyl groups attached as acetals to two hydroxyls of nonreducing lateral end groups of the capsular polysaccharides of Klebsiella serotypes K11 and K21. The R and S isomers of 4,6-O-pyruvyl-D-alpha-methylgalactoside were used as inhibitors with appropriate polysaccharide antigens and antisera to the two serotypes. The R isomer was a potent inhibitor of precipitation in both antisera, showing that the pyruvylgalactosyl residues in the polysaccharides of both K11 and K21 are in the R form, in which the methyl group of pyruvyl is equatorial to the plane of the acetal ring.