Kinetic determinants of the interaction of enoyl-ACP reductase from Plasmodium falciparum with its substrates and inhibitors

Abstract

We have recently demonstrated that Plasmodium falciparum, unlike its human host, has the type II fatty acid synthase, in which steps of fatty acid biosynthesis are catalyzed by independent enzymes. This difference could be successfully exploited in the design of drugs specifically targeted at the different enzymes of this pathway in P. falciparum, without affecting the corresponding enzymes in humans. The importance of enoyl-ACP reductase (FabI) in the fatty acid biosynthesis pathway makes it an important target in antimalarial therapy. We report here the initial characterization of Plasmodium FabI expressed in Escherichia coli. The K_m values of the enzyme for crotonyl-CoA and NADH were derived as 165 and 33 μM, respectively. Triclosan shows competitive kinetics with respect to NADH but is uncompetitive with respect to NAD⁺, which shows that the binding of triclosan to the enzyme is facilitated in the presence of NAD⁺.