Enzymes of Carbohydrate Metabolism in Four Human Species of Leishmania: A Comparative Survey*

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Abstract
The occurrence and levels of activity of various enzymes of carbohydrate catabolism in culture forms (promastigotes) of 4 human species of Leishmania (L. brasiliensis, L. donovani, L. mexicana and L. tropica) were compared. These organisms possessed enzymes of the Embden-Meyerhof pathway but lacked lactate dehydrogenase. No evidence could be found for the production of lactic acid by growing cultures, and lactic acid could not be detected either in cell-free preparations or after incubation of cell-free extracts with pyruvate and NADH under appropriate conditions. All 4 spp. possessed .alpha.-glycerophosphate dehydrogenase and .alpha.-glycerophosphate phosphatase which together could regenerate NAD, thus compensating for the absence of lactate dehydrogenase. The oxidative and nonoxidative reactions of the hexose monophosphate pathway were present in all 4 spp. Cell-free extracts had pyruvate dehydrogenase activity which allowed the entry of pyruvate into and its subsequent oxidation through the tricarboxylic acid cycle. All enzymes of this cycle, including a thiamine pyrophosphate dependent .alpha.-ketoglutarate dehydrogenase, were present. Both NAD and NADP-linked malate dehydrogenase activities were present. The isocitrate dehydrogenase was NADP specific. There is an active glutamate dehydrogenase which could compete with .alpha.-ketoglutarate dehydrogenase for the common substrate (.alpha.-ketoglutarate). Replenishment of C4 acids was accomplished by heterotrophic CO2 fixation catalyzed by pyruvate carboxylase. All 4 spp. had high levels of NADH oxidase activity. Several enzymes, so far not found in any Leishmania spp., were demonstrated. These were phosphoglucose isomerase, triose phosphate isomerase, fructose-1, 6-diphosphatase, 3-phosphoglycerate kinase, enolase, .alpha.-glycerophosphate dehydrogenase, .alpha.-glycerophosphate phosphatase, pyruvate dehydrogenase complex, citrate synthase, aconitase, .alpha.-ketoglutarate dehydrogenase, glutamate dehydrogenase and NADH oxidase.