Characterization and inhibition of dihydrofolate synthetase from Neisseria gonorrhoeae

Dihydrofolate synthetase (EC 6.3.2.12) from N. gonorrhoeae was isolated and enzyme characteristics were determined. The purified enzyme was found quite stable when stored at -60 degrees C. About 50% of the enzyme activity was destroyed within 6 weeks when kept at 4 degrees C. Maximum velocity was observed at pH 9.3. The enzyme required a monovalent cation, K+ or NH4+, and divalent cation, Mg2+ or Mn2+, for its function. ATP at 5 mM concentration gave maximum activity. Km values for dihydropteroate and L-glutamate at pH 9.3 were 3.5 X 10(-5) M and 6.5 X 10(-4) M, respectively. Patterns of product inhibition by dihydrofolate were found to be non-competitive with respect to dihydropteroate, having a Ki value of 5.1 +/- 0.8 X 10(-4) M, and competitive with respect to L-glutamate, having a Ki value of 6.2 X 10(-4) M.