Alterations in Dihydropteroate Synthetase in Cell-Free Extracts of Sulfanilamide-Resistant Neisseria meningitidis and Neisseria gonorrhoeae

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Abstract
Extracts from Neisseria meningitidis and N. gonorrhoeae with varying susceptibility to sulfanilamide have been investigated for dihydropteroate synthetase activity. Sulfanilamide was a competitive inhibitor of dihydropteroate synthetase with respect to p -aminobenzoate in extracts from both species. Though the K m for p -aminobenzoate was unaffected, the K i for sulfanilamide increased and the V max decreased as the strains' resistance to sulfanilamide increased. Temperature studies have revealed differences in the dihydropteroate synthetase from N. meningitidis and N. gonorrhoeae . A direct relationship was observed between the minimal inhibitory concentration of sulfanilamide determined in vitro and the ratio of K i /K m . This ratio may be a molecular explanation of sulfanilamide resistance for both N. meningitidis and N. gonorrhoeae .