The active sites of rabbit antibodies to the Group A streptococcal polysaccharide have been affinity labeled with a reagent (p-diazoniumphenyl-β-N-acetylglucosaminide) based on the terminal immunodominant monosaccharide of the Group A polysaccharide. Isoelectric focusing of radiolabeled antibodies showed that two of six antipolysaccharide antisera contained small amounts of restricted individual antibody components which affinity labeled with very high specificity. Most of the antibodies, including major restricted components which stand out from a heterogeneous background in isoelectric focusing, were affinity labeled with low specificit. The antipolysaccharide antibodies were purified by affinity chromatography on Sepharose conjugated with p-aminophenyl-β-N-acetylglucosaminide.
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