Para-Aminobenzoic Acid Inhibitors

Dihydropteroate synthase catalyses the condensation of para-aminobenzoate with 6-hydroxymethyl-7,8-dihydropterin diphosphate to form 7,8-dihydropteroate, the immediate precursor of folate derivatives, and is step 1 of 2 in the bacterial tetrahydrofolate biosynthesis pathway. Drugs in this class compete with para-aminobenzoate for that enzyme: UniProt records that sulfonamide drugs, for example sulfamethoxazole, act as competitive inhibitors of dihydropteroate synthase activity, and the sulfamethoxazole/trimethoprim label states that sulfamethoxazole inhibits bacterial synthesis of dihydrofolic acid by competing with para-aminobenzoic acid. Paired with a dihydrofolate reductase inhibitor, the two drugs block two consecutive steps in the biosynthesis of nucleic acids and proteins essential to many bacteria. The class is wider than the sulfonamides alone: the cited list also holds dapsone and aminosalicylic acid.