Trypanothione synthetase, a validated drug target, synthesizes trypanothione from glutathione and spermidine. Here we report the gene cloning, expression, characterization and inhibition studies of trypanothione synthetase from Leishmania donovani (Ld TryS). The purified recombinant Ld TryS enzyme obeyed Michaelis-Menten kinetics. High substrate inhibition was observed with glutathione ( K m =33.24 μ m , k cat =1.3 s -1 , K i =866 μ m ). The enzyme shows simple hyperbolic kinetics with fixed glutathione concentration and with other substrates limiting K m values for Mg. ATP and spermidine of 14.2 μ m and 139.6 μ m , respectively. Ld TryS was also screened for inhibitors. Tomatine, conessine, uvaol and betulin were identified as inhibitors of the enzyme and were tested for leishmanicidal activity. Finally, the effect of Ld TryS inhibitors on redox homeostasis of the parasite gives a broader picture of their action against leishmaniasis.
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