Regulation of aerobic fermentation in Leishmania donovani promastigotes by NADP⁺-dependent malic enzyme

Abstract

NADP⁺-dependent malic enzyme (decarboxylating) was extracted from Leishmania donovani promastigotes with Triton X-100. The enzyme was specific for NADP⁺ and did not decarboxylate oxaloacetate (OA). The substrate activity relationship was hyperbolic for both L-malate and NADP⁺, and K_mvalues were calculated as 0 18 and 0.012 mM, respectively. The enzyme exhibited a broad pH optimum of 7.5–8.0. Pyruvate, NADPH and OA inhibited the reaction in a competitive manner with apparent K_i values of 0.2, 0.04 and 0.04 mM, respectively, while oxalate inhibition was of the mixed type.

The kinetic results obtained indicate that malic enzyme is involved in the regulation of carbon flow towards aerobic fermentation, complete oxidation of dicarboxylic acids or biosynthetic purposes.