Tetroxoprim - a new inhibitor of bacterial dihydrofolate reductase

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Abstract
Dihydrofolate-reductase of E. coli MRE 600 was concentrated 16-fold by ionexchange chromatography. The Michaelis constant (K m ) obtained for dihydrofolate was 2·7 × 10 -5 M. The inhibition constant (K i ) obtained for tetroxoprim were 3·2 × lO -9 M and 4·0 × 10 -9 M for trimethoprim, respectively. The Michaelis constant of commercial dihydrofolate-reductase from bovine liver, determined for the substrate dihydrofolate was 1·2 × 10 -4 M and was independent of additional inhibitors in low concentrations. It was shown that the concentrations of tetroxoprim and trimethoprim which cause a 50% inhibition of the mammalian enzyme, are at least 60,000 and 50,000 fold higher than those which cause appropriate inhibition ofthe bacterial enzyme.

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