Azoproteins prepared with p-aminophenyl-ß-N-acetyl-glucosaminide react in precipitin tests with Group A streptococcal antisera. The reaction is nonreciprocal, and antisera to the azoprotein do not react with Group A carbohydrate.

Phenyl-N-acetyl-glucosaminides inhibit the reaction of Group A carbohydrate with homologous antisera and with antisera to the azoprotein. The ß-anomer is more effective as an inhibitor than the α-anomer.

Formation by a soil bacillus of the enzyme which removes N-acetyl-glucosamine from Group A carbohydrate is induced by phenyl-ß-N-acetyl-glucosaminide but not by the α-compound. The enzyme, like the glucosaminidase of emulsin, appears to be specific for ß-glucosaminides.

Neither the induced enzyme nor emulsin effectively remove all of the N-acetyl-glucosamine from the azoprotein antigens.

The findings support the view that ß-N-acetyl-glucosaminide side chains represent the major antigenic determinant of Group A streptococcal carbohydrate.

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