Enzymes of carbohydrate metabolism in four human species of Leishmania: a comparative survey

Identification of protein profile in metacyclic and amastigote-like stages of Leishmania tropica: a proteomic approach

Leishmaniasis is a tropical disease that leads to various clinical phenotypes. This study aimed to investigate protein expression changes in metacyclic and amastigote-like stages of L. tropica isolated from Iranian cutaneous leishmaniasis patients. Isolated samples were cultured and species type identified using PCR–RFLP technique. The promastigotes were grown in RPMI1640 media and differentiated to metacyclic and amastigote-like forms, followed by the extracted proteins of both successive stages carried out for proteomics and bioinformatics analysis. Using SWATH-MS quantitative proteomics technique, a total 176 and 155 distinct proteins were identified in metacyclic and axenic amastigote stages, respectively. Of these, 65 proteins were altered significantly (p-value < 0.05 and fold change ≥ 2) between studied stages. Several gene ontology (GO) categories were enriched for biological process during conversion of metacyclic promastigotes into amastigote-like, which “metabolic process” (GO: 0044281, P-Value: 6.52e-5), and “translation” (GO: 0006412, p-value: 5.01e–14) were disclosed as the top category in up and down-regulated proteins, respectively. Also, the KEGG pathway analysis indicated “metabolic pathways” and “ribosome” term as the most important pathways in up and down-regulated proteins, respectively. According to protein interaction network analysis, enolase (ENOL) has been detected as main hub proteins during differentiation, followed by Putative NADH-dependent fumarate reductase (LmjF.35.1180) and 40S ribosomal protein S2 (LmjF.32.0450). Overall, protein changes possibly play important roles in L. tropica biology. Anabolic pathways were down-regulated, whereas catabolic pathways were up-regulated during L. tropica differentiation. These protein expression changes could provide parasite survival in host macrophages, and could use as novel potential drug and vaccine targets for leishmaniasis.

Graphical Abstract

Workshop no. 1. Alternate metabolic pathways in protozoan energy metabolism

The purpose of this workshop was to collect together colleagues investigating the intermediary metabolism of protozoa, with a view to discussing those pathways involved in energy metabolism and the production of ATP and other high-energy compounds, together with the factors affecting energy balance. The aspects of energy metabolism chosen for discussion comprised the metabolic pathways ranging from the strictly anaerobic to highly oxidative; subcellular compartmentation of these pathways within the protozoa; the functional role of these pathways including a consideration of aero-tolerance; and the use of inhibitors as biochemical probes and potential chemotherapeuticagents. Hopefully this approach has produced a broad 'over-view' of important areas of protozoan energy metabolism which will enable both the specialist and non-specialist to appreciate the similarities and differences between the metabolic behaviour of a range of protozoa.

Depot Subcutaneous Injection with Chalcone CH8-Loaded Poly(Lactic-Co-Glycolic Acid) Microspheres as a Single-Dose Treatment of Cutaneous Leishmaniasis

Conventional chemotherapy of cutaneous leishmaniasis (CL) is based on multiple parenteral or intralesional injections with systemically toxic drugs. Aiming at a single-dose localized therapy, biodegradable poly(lactic-co-glycolic acid) (PLGA) microparticles loaded with 7.8% of an antileishmanial nitrochalcone named CH8 (CH8/PLGA) were constructed to promote sustained subcutaneous release. In vitro, murine macrophages avidly phagocytosed CH8/PLGA smaller than 6 μm without triggering oxidative mechanisms. Upon 48 h of incubation, both CH8 and CH8/PLGA were 40 times more toxic to intracellular Leishmania amazonensis than to macrophages. In vivo, BALB/c were given one or three subcutaneous injections in the infected ear with 1.2 mg/kg of CH8 in free or CH8/PLGA forms, whereas controls received three CH8-equivalent doses of naked PLGA microparticles or meglumine antimoniate (Glucantime; Sanofi-Aventis). Although a single injection with CH8/PLGA reduced the parasite loads by 91%, triple injections with free CH8 or CH8/PLGA caused 80 and 97% reductions, respectively, in relation to saline controls. Meglumine antimoniate treatment was the least effective (only 36% reduction) and the most toxic, as indicated by elevated alanine aminotransferase serum levels. Together, these findings show that CH8/PLGA microparticles can be effectively and safely used for single-dose treatment of CL.

Metabolic changes in glucose transporter-deficient Leishmania mexicana and parasite virulence

Leishmania mexicana are parasitic protozoa that express a variety of glycoconjugates that play important roles in their biology as well as the storage carbohydrate beta-mannan, which is an essential virulence factor for survival of intracellular amastigote forms in the mammalian host. Glucose transporter null mutants, which are viable as insect form promastigotes but not as amastigotes, do not take up glucose and other hexoses but are still able to synthesize these glycoconjugates and beta-mannan, although at reduced levels. Synthesis of these carbohydrate-containing macromolecules could be accounted for by incorporation of non-carbohydrate precursors into carbohydrates by gluconeogenesis. However, the significantly reduced level of the virulence factor beta-mannan in the glucose transporter null mutants compared with wild-type parasites may contribute to the non-viability of these null mutants in the disease-causing amastigote stage of the life cycle.

Substrate preferences and glucose uptake in glibenclamide-resistant Leishmania parasites

Several drug-resistant mammalian cell types exhibit increased glycolytic rates, preferential synthesis of ATP through oxidative phosphorylation, and altered glucose transport. Herein we analyzed the influence of parasite growth phase on energy substrate uptake and use in a Leishmania strain [NR(Gr)] selected for resistance against glibenclamide. Glibenclamide is an ABC-transporter blocker which modulates the function of glucose transporters in some mammalian cells. Our results demonstrate for the first time that compared to glibenclamide-sensitive Leishmania, exponential phase glibenclamide-resistant parasites exhibit decreased use of glucose as energy substrate, decreased glucose uptake and decreased glucose transporter expression. However, compared to glibenclamide-sensitive cells, stationary phase resistant parasites display an increased use of amino acids as energy substrate and an increased activity of the enzymes hexokinase, phosphoglucose isomerase, and especially NAD(+)-linked glutamate dehydrogenase. These results suggest that drug resistance in Leishmania involves a metabolic adaptation that promotes a stage dependent modulation of energy substrate uptake and use as a physiological response to the challenge imposed by drug pressure.

Transketolase from Leishmania mexicana has a dual subcellular localization

Transketolase has been characterized in Leishmania mexicana. A gene encoding this enzyme was identified and cloned. The gene was expressed in Escherichia coli and the protein was purified and characterized. An apparent K(m) of 2.75 mM for ribose 5-phosphate was determined. X-ray crystallography was used to determine the three-dimensional structure of the enzyme to a resolution of 2.2 A (1 A identical with 0.1 nm). The C-terminus of the protein contains a type-1 peroxisome-targeting signal, suggestive of a possible glycosomal subcellular localization. Subcellular localization experiments performed with promastigote forms of the parasite revealed that the protein was predominantly cytosolic, although a significant component of the total activity was associated with the glycosomes. Transketolase is thus the first enzyme of the nonoxidative branch of the pentose phosphate pathway whose presence has been demonstrated in a peroxisome-like organelle.

Expression and regulation of mitochondrial uncoupling protein 1 from brown adipose tissue in Leishmania major promastigotes

Rat uncoupling protein 1 (UCP1) was successfully translated in transfected Leishmania major promastigotes. Immune electron microscopy revealed that the protein was exclusively in the mitochondria. UCP1 expression was about 350,000 copies per promastigote, accounting for 4.7% of the total mitochondrial protein. In intact parasites, expression of UCP1 induced a slight increase in respiratory rate and a modest decrease in mitochondrial membrane potential (delta psi(m)). In contrast, in digitonin-permeabilized parasites, a significantly lower value both in delta psi(m) (57 +/- 10 vs 153 +/- 12 mV) and respiratory control ratio (0.99 vs 1.54) were observed for UCP1 versus control parasites, although when UCP1 activity was inhibited by bovine serum albumin (BSA) and GDP, control values were restored. Therefore, a fully functional UCP1 was present and only partially inhibited in vivo by endogenous purine nucleotides. However, neither ATP levels, growth rate nor mitochondrial protein import differed significantly between both types of parasites. Expression of the pore-like mutant UCP1 delta 9 was deleterious to the organism. Consequently, Leishmania was capable of expressing and importing into mitochondria proteins from higher eukaryotes lacking an N-terminal targeting pre-sequence as UCP1. As described previously, parasite metabolism had only a limited tolerance to mitochondrial disfunction. Transfection of Leishmania with foreign proteins which play an important regulatory role in metabolism is a useful tool to study both parasite metabolism in general, and alternative pathways involved in maintaining internal homeostasis.

The effects of co-cultivation with the acetogen Acetitomaculum ruminis on the fermentative metabolism of the rumen fungi Neocallimastix patriciarum and Neocallimastix sp. strain L2

The effects of co-cultivation with the hydrogen-utilizing acetogenic bacterium Acetitomaculum ruminis on the fermentative activities of the rumen fungi Neocallimastix patriciarum or Neocallimastix sp. L2 were investigated. In both co-cultures acetate production increased, making it the predominant fermentation product, as the accumulation of lactate, formate, ethanol, H2 and (in the case of Neocallimastix sp. L2) succinate all decreased. The effects of co-cultivation with Methanobrevibacter smithii were more pronounced. Decreased activities of lactate dehydrogenase, alcohol dehydrogenase and (in the case of Neocallimastix sp. L2) fumarate reductase accompanied the shift in fermentation product formation. The rate of glucose utilization and the fungal biomass yield were also increased in the co-culture.

Energy metabolism in Leishmania

Alanine plays a key role in the response of promastigotes to osmotic stress and to hypoxia. It is rapidly released in response to hypo-osmolality, is consumed from its large intracellular pool under iso-osmotic conditions even in the presence of glucose, and is synthesized under hyperosmotic conditions even in the absence of glucose. Its rate of oxidation, in the presence or absence of any of ten other amino acids tested, is strongly inhibited by hyperosmolality. Glucose oxidation is also inhibited by hyperosmolality, but to a lesser extent than that of alanine, and is inhibited by alanine, glutamate, and aspartate. Hyperosmolality also inhibits the incorporation of label from [2-14C]acetate into the putative storage carbohydrate, mannan, which occurs via the glyoxylate bypass and the as yet unexplored "mannoneogenic" pathway. The rates of glycolysis and of oxidation of several amino acids decrease with increasing culture age, but the capacity to oxidize fatty acids increases, and in cells from 3-day stationary phase cultures hyperosmolality enhances rather than inhibits alanine oxidation.

Evaluation of antileishmanial activity of trans-aconitic acid

TAA, an inhibitor of the enzyme aconitase, inhibits the growth of L. donovani promastigotes. Morphogenic transformation of the amastigote to the promastigote (table; see text) form in vitro was also inhibited by 2 mM TAA. TAA also reduced multiplication of the parasite in macrophage culture. In the hamster model of leishmania, TAA significantly reduced the parasitic burden of liver. In acute toxicity tests with BALB/c mice no deaths were recorded even at a dose level of 2 g/kg body wt/day.

Methylglyoxal-catabolizing enzymes of Leishmania donovani promastigotes

Methylglyoxal is a toxic metabolite with growth inhibitory properties against Leishmania donovani promastigotes. We have shown in the present study that both log and stationary phase promastigotes of L. donovani can catabolize methylglyoxal to D-lactate as the major end product. The specific activity of methylglyoxal reductase was found to be the highest of all the catabolic enzymes. In contrast, the anabolic pathway for methylglyoxal could not be detected. Moreover, when control promastigotes or promastigotes in which the glycolytic pathway was inhibited were incubated with glucose, glycerol or dihydroxyacetone phosphate as energy source, neither methylglyoxal nor D-lactate could be detected.

Metabolic interactions between glucose, glycerol, alanine and acetate in Leishmania braziliensis panamensis promastigotes

13C-nuclear magnetic resonance (NMR) spectroscopy was used to investigate the products of glycerol and acetate metabolism released by Leishmania braziliensis panamensis promastigotes and also to examine the interaction of each of these substrates with glucose or alanine. The NMR data were supplemented by measurements of the rates of oxygen consumption and substrate utilization, and of 14CO2 production from 14C-labeled substrate. Cells incubated with [2-13C]glycerol released acetate, succinate and D-lactate in addition to CO2. Cells incubated with acetate released only CO2. More succinate C-2/C-3 than C-1/C-4 was released from both [2-13C]glycerol and [2-13C]glucose, indicating that succinate was formed predominantly by CO2 fixation followed by reverse flux through part of the Krebs cycle. Some redistribution of the position of labeling was also seen in alanine and pyruvate, suggesting cycling through pyruvate/oxaloacetate/phosphoenolpyruvate. Cells incubated with combinations of 2 substrates consumed oxygen at the same rate as cells incubated with 1 or no substrate, even though the total substrate utilization had increased. When promastigotes were incubated with both glycerol and glucose, the rate of glucose consumption was unchanged but glycerol consumption decreased about 50%, and the rate of 14CO2 production from [1,(3)-14C]glycerol decreased about 60%. Alanine did not affect the rates of consumption of glucose or glycerol, but decreased 14CO2 production from these substrates by increasing flow of label into alanine. Although glucose decreased alanine consumption by 70%, it increased the rate of 14CO2 production from [U-14C]- and [l-14C]alanine by about 20%.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential energetic metabolism during Trypanosoma cruzi differentiation. I. Citrate synthase, NADP-isocitrate dehydrogenase, and succinate dehydrogenase

The activities of the mitochondrial enzymes citrate synthase (citrate oxaloacetatelyase, EC 4.1.3.7), NADP-linked isocitrate dehydrogenase (threo-Ds-isocitrate:NADP+ oxidoreductase (decarboxylating), EC 1.1.1.42), and succinate dehydrogenase (succinate: FAD oxidoreductase, EC 1.3.99.1) as well as their kinetic behavior in the two developmental forms of Trypanosoma cruzi at insect vector stage, epimastigotes and infective metacyclic trypomastigotes, were studied. The results presented in this work clearly demonstrate a higher mitochondrial metabolism in the metacyclic forms as is shown by the extraordinary enhanced activities of metacyclic citrate synthase, isocitrate dehydrogenase, and succinate dehydrogenase. In epimastigotes, the specific activities of citrate synthase at variable concentrations of oxalacetate and acetyl-CoA were 24.6 and 26.6 mU/mg of protein, respectively, and the Michaelis constants were 7.88 and 6.84 microM for both substrates. The metacyclic enzyme exhibited the following kinetic parameters: a specific activity of 228.4 mU/mg and Km of 3.18 microM for oxalacetate and 248.5 mU/mg and 2.75 microM, respectively, for acetyl-CoA. NADP-linked isocitrate dehydrogenase specific activities for epimastigotes and metacyclics were 110.2 and 210.3 mU/mg, whereas the apparent Km's were 47.9 and 12.5 microM, respectively. No activity for the NAD-dependent isozyme was found in any form of T. cruzi differentiation. The particulated succinate dehydrogenase showed specific activities of 8.2 and 39.1 mU/mg for epimastigotes and metacyclic trypomastigotes, respectively, although no significant changes in the Km (0.46 and 0.48 mM) were found. The cellular role and the molecular mechanism that probably take place during this significant shift in the mitochondrial metabolism during the T. cruzi differentiation have been discussed.

Trichomonas vaginalis: characterization of its glutamate dehydrogenase

An NADP-linked glutamate dehydrogenase (EC 1.4.1.4) was found in the soluble fraction of Trichomonas vaginalis. Its molecular weight was about 230,000 (gel filtration). The enzyme, partially purified by diafiltration and hydroxyapatite column chromatography, was heat stable (1 hr at 57 C). It catalyzed both the amination of alpha-ketoglutarate (mean Km 0.6 mM) and the deamination of glutamate (mean Km 1.2 mM) The optimum pH of the amination reaction was 6.7, and that of the deamination reaction was 8. Glutamate was a competitive inhibitor of the amination reaction (mean Ki 5.6 mM) and alpha-ketoglutarate a partially competitive inhibitor of the deamination reaction (mean Ki 0.45 mM). Both guanosine and inosine diphosphates (1 mM) increased the Km alpha-ketoglutarate fivefold (mean Ki's 0.3 and 0.4 mM, respectively). Guanosine diphosphate reduced the Km glutamate 40%. Adenosine di- and triphosphate (1 mM) were ineffective. Because the amination reaction displayed substrate inhibition, guanosine and inosine diphosphates were potent natural inhibitors, and ammonia released by deamination reactions would tend to raise pH (amination operative at acid pH), we hypothesize that the deamination reaction may predominate in the living organism.

Purification and characterization of a metabolite-regulated pyruvate kinase from Leishmania major promastigotes

The pyruvate kinase (ATP:pyruvate 2-O-phosphotransferase, EC 2.7.1.40) of Leishmania major promastigotes is a multimer of 59 kDa subunits having an Mr 181000. It is activated by its substrate phosphoenolpyruvate (PEP) in a positively cooperative manner, and heterotropically by fructose 1,6-bisphosphate (FBP). Kinetics with regard to the phosphate acceptor adenosine 5'-diphosphate (ADP), MgCl2, and KCl are hyperbolic and unaffected by FBP. The enzyme is strongly inhibited by the reaction product ATP, as well as GTP and ITP, and to a lesser degree by citrate. Of seven amino acids reported to inhibit the pyruvate kinases of other organisms, none have any effect on the L. major pyruvate kinase in vitro. The enzyme shows its maximum activity at pH 7.0 in the absence of FBP, and at pH 7.6 in its presence. Contrary to previous suggestions, the enzyme appears to be well-suited for a regulatory role in the metabolism of an aerobic organism capable of net glucose synthesis.

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

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 Km values were calculated as 0.18 and 0.12 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 Ki 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.

Products of Leishmania braziliensis glucose catabolism: release of D-lactate and, under anaerobic conditions, glycerol

Leishmania braziliensis panamensis promastigotes were incubated with glucose as the sole carbon source. About one-fifth of the glucose consumed under aerobic conditions was oxidized to CO2. Nuclear magnetic resonance studies with [1-13C]glucose showed that the other products released were succinate, acetate, alanine, pyruvate, and lactate. Under anaerobic conditions, lactate output increased, glycerol became a major product, and, surprisingly, glucose consumption decreased. Enzymatic assays showed that the lactate formed was D(-)-lactate. The release of alanine during incubation with glucose as the sole carbon source suggested that appreciable proteolysis occurred, consistent with our observation that a large amount of ammonia was released under these conditions. The discoveries that D-lactate is a product of L. braziliensis glucose catabolism, that glycerol is produced under anaerobic conditions, and that the cells exhibit a "reverse" Pasteur effect open the way for detailed studies of the pathways of glucose metabolism and their regulation in this organism.

Identification of a major 72 kilodalton surface antigen in twelve isolates of Leishmania braziliensis braziliensis

The study of the surface antigens of Leishmania braziliensis braziliensis revealed a great homogeneity among ten strains isolated from Bolivia and two reference strains from Brazil and Belize. A 72 kDa major protein, present in all L. b. braziliensis strains, was recognized by both cutaneous and mucocutaneous human sera, but was not recognized by Kala-azar and chagasic sera. No cross-reactive antigens were found among strains of Leishmania braziliensis guyanensis, Leishmania braziliensis panamensis, Leishmania mexicana amazonensis and Leishmania donovani chagasi testing these strains with hamster and human anti-L. b. braziliensis sera. Moreover, these strains possessed major antigens with molecular weights different from those of L. b. braziliensis strains. A microheterogeneity of L. b. braziliensis surface antigens was detected for the high molecular weight antigens and seemed to be related to the isoenzymic microheterogeneity.

End products and enzyme levels of aerobic glucose fermentation in trypanosomatids

Trypanosoma cruzi (epimastigotes), Crithidia fasciculata and Leishmania mexicana (promastigotes) were grown in a brain-heart-tryptose medium supplemented with heat-inactivated fetal calf serum. T. cruzi and C. fasciculata utilized glucose completely during the log phase of growth, whereas L. mexicana used significant amounts of the carbohydrate only at the end of the log phase and at the beginning of the stationary phase. In all cases glucose consumption resulted in excretion of succinate, and much smaller amounts of acetate. C. fasciculata and L. mexicana produced very small amounts of pyruvate. C. fasciculata produced ethanol, which was taken up again and metabolysed after glucose was exhausted. Lactate and malate were not produced. The cells were disrupted by sonic disintegration, and the activities of some key enzymes of carbohydrate and amino acid catabolism were assayed in the whole homogenates. Phosphoenolpyruvate carboxykinase was present in the three organisms; L. mexicana presented the highest specific activity. The activity of this enzyme was maximal during glucose consumption, and slightly decreased after glucose was exhausted. This suggests that the role played by the enzyme is glycolytic and not gluconeogenic; the latter is the case in most higher organisms. Hexokinase and pyruvate kinase presented their highest levels in C. fasciculata and T. cruzi during glucose consumption. L. mexicana, which was in active glycolysis during the whole experimental period, presented the highest specific activities of both enzymes. Citrate synthase, on the other hand, increased in C. fasciculata and, to a lesser extent, in T. cruzi, after glucose was exhausted; the enzyme could not be detected in L. mexicana. The NAD-linked glutamate dehydrogenase increased considerably in C. fasciculata and T. cruzi after glucose was exhausted, suggesting a catabolic role for the enzyme. This increase coincided with an increase in NH3 production by both organisms after glucose consumption. The NADP-linked glutamate dehydrogenase, on the other hand, presented a maximum about the time when glucose was exhausted, and then decreased again, which suggests a catabolic role for the enzyme. Both glutamate dehydrogenases had low activities in L. mexicana; this fits in well with the low NH3 production throughout the culture of this organism. The results are in good agreement with current ideas on the mechanism of aerobic glucose fermentation by trypanosomatids, and suggest that, under the experimental conditions used, both T. cruzi and C. fasciculata used glucose perferentially over amino acids for growth.

Leishmania mexicana: enzyme activities of amastigotes and promastigotes and their inhibition by antimonials and arsenicals

A major difference between the metabolism of Leishmania species amastigotes and cultured promastigotes was found in the area of CO2 fixation and phosphoenolpyruvate metabolism. Malate dehydrogenase (EC 1.1.1.37) and phosphoenolpyruvate carboxykinase (EC 4.1.1.49) were at much higher activities in amastigotes than promastigotes of both L. m. mexicana and L. donovani, whereas the reverse was true of pyruvate kinase (EC 2.7.1.40). Pyruvate carboxylase (EC 6.4.1.1) and malic enzyme (carboxylating) (EC 1.1.1.40) could not be detected in L. m. mexicana amastigotes. Promastigotes of L. m. mexicana had a high NAD-linked glutamate dehydrogenase activity in comparison to amastigotes, whereas NADP-linked glutamate dehydrogenase activity was detected only in amastigotes. Leishmania m. mexicana culture promastigotes were killed in vitro by the trivalent antimonial Triostam (LD50, 20 micrograms/ml) and the trivalent arsenical melarsen oxide (LD50, 20 micrograms/ml), but they were unaffected by Pentostam. Neither antimonial drug significantly inhibited leishmanial hexokinase (EC 2.7.1.2), phosphofructokinase (EC 2.7.1.11), pyruvate kinase, malate dehydrogenase or phosphoenolpyruvate carboxykinase, whereas melarsen oxide was a potent inhibitor of all the enzymes tested except phosphoenolpyruvate carboxykinase.

The occurrence of glycosomes (microbodies) in the promastigote stage of four major Leishmania species

Evidence is presented for the occurrence of glycosomes (organelles resembling peroxisomes) in four major species of Leishmania (viz. L. major, L.m. mexicana, L. b. braziliensis and L. donovani), based on latency as well as differential and isopycnic centrifugation studies. The enzymes involved in glycolysis; (hexokinase, phosphoglucose isomerase, phosphofructokinase, fructose-1,6-bisphosphate aldolase, triosephosphate isomerase, glyceraldehyde-phosphate dehydrogenase and phosphoglycerate kinase); glycerol metabolism (sn-glycerol-3-phosphate dehydrogenase and glycerol kinase); carbon dioxide fixation (phosphoenolpyruvate carboxykinase and possibly malate dehydrogenase); together with an enzyme involved in the beta-oxidation of fatty acids (3-beta-hydroxybutyryl coenzyme A dehydrogenase); a key enzyme in the synthesis of ether lipids (dihydroxyacetone phosphate acyltransferase) as well as the ADP utilising enzyme adenylate kinase, were all found associated, at least in part, with a subcellular organelle which had a buoyant density in sucrose gradients of 1.21 to 1.24 g cm-3. Little variance in enzyme composition was found between the different species of Leishmania or in comparison with other members of the Trypanosomatidae, supporting the unifying principle that glycosomes are a unique characteristic of this family. The occurrence of important catabolic, anabolic and anaplerotic pathways in the glycosomes of Leishmania renders them prime targets for chemotherapy.

Regulation of energy metabolism in Trypanosoma (Schizotrypanum) cruzi epimastigotes. I. Hexokinase and phosphofructokinase

Hexokinase (ATP: hexose 6-phosphotransferase, E.C.2.7.1.1) and phosphofructokinase (ATP:fructose-6-phosphate 1-phosphotransferase, E.C.2.7.1.11), two key regulatory enzymes of the glycolytic pathway in vertebrate cells, have been isolated and partially purified from Trypanosoma (Schizotrypanum) cruzi epimastigotes. Both enzymes are associated with particles sedimentable at 105 000 X gav for 1 h and have a high degree of latency; they can be solubilized by sonication. Hexokinase catalyses the phosphorylation of a series of monosaccharides at the following relative rates: D-glucose (100) congruent to D-fructose (97) greater than 2-deoxy-D-glucose (72) congruent to mannose (69) greater than 2-amino-D-glucose (63) greater than 3-O-methyl-D-glucose (21). Very little or no phosphorylating activity was found for D-galactose, N-acetyl-2-amino-D-glucose or 1-alpha-methyl-D-glucose. D-Glucose phosphorylation at fixed ATP concentration follows simple Michaelis-Menten kinetics with Km = 40 microM and Vmax = 440 nmol min-1 mg-1 protein. D-Mannose, 2-deoxy-D-glucose and N-acetyl-2-amino-D-glucose act as competitive inhibitors of glucose phosphorylation, suggesting a single kinase. Mg2+-ATP is the preferred phosphoryl donor, ITP and GTP being much less effective. T. cruzi hexokinase is not inhibited by D-glucose 6-phosphate, or by any of the following compounds (2 mM):D-fructose 6-phosphate, D-fructose 1,6-diphosphate, D-glucose 1,6-diphosphate, phosphoenol pyruvate, L-malate and citrate. Phosphofructokinase displays simple Michaelis-Menten kinetics with no evidence of sigmoidicity with respect to D-fructose 6-phosphate at all ATP concentrations tested, giving a Km of 1.31 mM and Vmax = 400 nmol min-1 mg-1 protein at optimal ATP levels. With respect to ATP, the enzyme exhibits Michaelis-Menten kinetics at low concentration (less than 1 mM) of the substrate (Km = 40 microM at 5 mM MgCl2, pH 7.4). A moderate inhibition is observed at high ATP levels (70% of maximal activity at 2 mM). GTP can substitute for ATP as the phosphoryl donor (Km = 79 microM under the same conditions), but produces only very small inhibitory effects at high concentrations. 5'-AMP activates the enzyme by decreasing its Km with respect to D-fructose 6-phosphate without affecting Vm. Other well-known regulators of the activity of this enzyme in procaryote and vertebrate systems such as citrate, phosphoenol pyruvate, ammonium and phosphate ions have no effect in T. cruzi.

Regulation of energy metabolism in Trypanosoma (Schizotrypanum) cruzi epimastigotes. II. NAD+-dependent glutamate dehydrogenase

Trypanosoma (Schizotrypanum) cruzi epimastigotes (EP stock) grown in complex LIT medium rapidly consume the glucose present but, under aerobic conditions, continue growth in its absence with the concomitant excretion of ammonia, suggesting the utilization of amino acids for energy production. A search for metabolic pathways responsible for amino acid oxidation led to the detection of a NAD+-dependent glutamate dehydrogenase (L-glutamate:NAD+ oxidoreductase, E.C.1.4.1.2) which is different from an NADP+-dependent enzyme previously reported. The enzyme has been partially purified and its kinetic and regulatory properties studied in both directions of the reaction. Km values were 3.6 mM for alpha-ketoglutarate, 0.170 mM for NADH and 16 mM for NH+4, Vmax = 0.67 mumol min-1/mg-1 protein for aminative reduction; Km values were 23.5 mM for L-glutamate and 2.9 mM for NAD+, Vmax = 0.02 mumol min-1 mg-1 protein for deaminative oxidation, Tris buffer, pH 7.6. The enzyme is strongly inhibited by ATP, GTP, ADP and GDP (50% inhibition at 0.75 mM ATP, 3 mM MgCl2). S-Acetyl-CoA is also a potent inhibitor of the enzyme. The results demonstrate the presence of a specific pathway for the oxidation of amino acids, which is tightly regulated by the energy charge and the Krebs cycle activity in T. cruzi epimastigotes.

Enzymes of carbohydrate metabolism in Leishmania donovani amastigotes

A method for the isolation of Leishmania donovani amastigotes from infected hamster spleen and liver tissues is described. Over 85% of the isolated amastigotes were viable as judged by acridine orange-ethidium bromide staining and in vitro transformation to the promastigote form. A comprehensive survey of the enzymes of carbohydrate metabolism in L. donovani amastigotes and promastigotes was conducted. Amastigotes and promastigotes possess all of the enzymes of the Embden-Meyerhof pathway, hexose monophosphate shunt, and tricarboxylic acid cycle. Cell-free extracts of both forms demonstrate an active glutamate dehydrogenase, thus linking activity which permits entry of pyruvate into the tricarboxylic acid cycle. Both forms demonstrate an active glutamate dehydrogenase, thus linking amino acid metabolism with carbohydrate metabolism. Pyruvate carboxylase, the enzyme responsible for replenishment of C4 acids by heterotrophic CO2 fixation into pyruvate, was also demonstrable in the tissue and insect forms. In general, activities of promastigote enzymes are higher than the amastigote enzymes. Differences between the vertebrate (amastigote) and invertebrate (promastigote) forms in their potential to utilize carbohydrates as substrates would appear to be quantitative rather than qualitative.

The free amino acid pool in Leishmania tropica promastigotes

The principal constituents of the free amino acid pool in Leishmania tropica promastigotes include alanine, glycine, serine, threonine, alpha-aminobutyric acid and ethanolamine. Changes in levels of the pool constituents during starvation, nutrient supplementation and treatment with a metabolic inhibitor (sodium fluoride) were followed. Several enzymes capable of converting amino acids to Krebs cycle intermediates were identified. It is suggested that during prolonged starvation which is accompanied by enhanced proteolysis, these enzymes enable the cells to utilize endogenous amino acids as carbon and energy sources. This is compatible with previous reports that Leishmania promastigotes in culture could grow on amino acids as growth substrates when carbohydrates are totally lacking.

Rapid identification of Leishmania species by specific hybridization of kinetoplast DNA in cutaneous lesions

Kinetoplast DNA (kDNA) was isolated from various species of the protozoic parasite Leishmania and analyzed by nucleic acid hybridization to detect species-related heterogeneity of kDNA. Purified DNA isolated from L. mexicana and L. braziliensis displayed no homology in nucleic acid hybridization studies. These results confirmed that rapid kDNA sequence change and evolution is occurring in New World species of Leishmania and suggested that such isolated kDNA could be used as a specific hybridization probe for the rapid identification of Leishmania species by using whole organisms. This work further demonstrates that such species-specific identification is feasible on isolated Leishmania promastigotes and, more important, directly on tissue touch blots derived from the cutaneous lesion. Thus, specific hybridization of isolated kDNA provides the basis for a rapid, accurate method for the diagnosis of human leishmaniasis directly from infected tissue.

A comparative study of Leishmania mexicana amastigotes and promastigotes. Enzyme activities and subcellular locations

Leishmania mexicana mexicana amastigotes have been shown to contain greater activities than promastigotes of the enzymes that catalyse the beta-oxidation of fatty acids, but lower activities of several glycolytic enzymes, with the activity of pyruvate kinase being especially low. The results suggest the beta-oxidation of fatty acids is relatively more important to Leishmania amastigotes than promastigotes, whereas the reverse is true for glycolysis. Succinic dehydrogenase and peptidase activities were much higher in promastigotes than amastigotes. The activities of glucose-6-phosphatase, fructose-1,6-bisphosphatase, acid phosphatase and glucose-6-phosphate dehydrogenase varied less, although in each case the activity was significantly lower in the mammalian stage. A method for lysing and fractionating L. m. mexicana promastigotes has been developed. Using this procedure it has been established that many of the glycolytic and functionally related enzymes are located in cell organelles, that hexokinase is intimately connected with the particulate part of the parasite, and that the microsomal fraction of L. m. mexicana is very different in composition from the microsomes of mammalian liver cells.

Partial purification and characterization of particulate acid phosphatase of Leishmania donovani promastigotes

1. More than 90% of the total acid phosphatase activity in a sonicate of L. donovani promastigotes is contained in a particulate fraction (200,000 X g 30 min). The enzyme can be quantitatively extracted and solubilized with the aid of Triton X-100 (0.2 g/100 ml) and purified over 200-fold with 54% yield by chromatography on DEAE-Sephadex, QAE-Sephadex, Sepharose 4B and concanavalin-A Sepharose. 2. The phosphatase is a true acid hydrolase (pH optimum, 5.0-5.5) and has a rather broad substrate specificity; it will catalyze the hydrolysis of 4-methylumbelliferylphosphate, thymolphthalein diphosphate, pyridoxal phosphate, fructose 1,6-diphosphate, glucose 6-phosphate, glucose 1-phosphate, ADP and AMP. 3. It is a large (170,000 daltons in the presence of Triton X-100), stable and acidic enzyme (pI = 4.1) that has the electrophoretic mobility of a type zero or type 1 isoenzyme in acid (pH 4.3) polyacrylamide gels. 4. The enzyme is inhibited by sodium fluoride, 2-mercaptoethanol and mumolar amounts of a number of polyanionic molybdenum and heavy metal complexes that include the following: [C(NH2)3]4[(C3H7O3PO3)2Mo5O15] X 3H2O, [C(NH2)3]2[(C6H5)2AsMo4O15H] X H2O, (NH4)4[SiMo12O40] X H2O and (NH4)6[P2Mo18O62] X 9H2O. 5. L. donovani promastigotes contain very low levels of 10 other acid pH optimum hydrolytic enzymes, with the exception of modest levels of alpha-fucosidase.

Respiration of Leishmania mexicana amastigotes and promastigotes

Promastigotes of Leishmania mexicana mexicana recently derived from amastigotes by transformation in vitro respired at a rate (17 nmol O2/min per 10(8) parasites) 4-5 times higher than that of amastigotes, but when the difference in cell protein content between the two preparations was taken into account the rates were not significantly different (32 nmol O2/min per mg protein). The respiration of both amastigotes and promastigotes was sensitive to cyanide, azide, antimycin A, 2-n-heptyl-4-hydroxyquinoline-N-oxide and high concentrations of amytal, but insensitive to rotenone and salicyl-hydroxamic acid, indicating that the two developmental forms possess a similar cytochrome-containing respiratory chain. D-Glucose and non-esterified fatty acids stimulated promastigote respiration and amastigote transformation to promastigotes in vitro; possibly these substances are important exogenous energy substrates for both forms of the parasites. Amino acids (incuding L-proline) and proteins did not appear to be used as energy substrates. The respiration rate of promastigotes was found to rise significantly upon continued sub-culture in vitro; at the same time cell size and protein content increased.

Some methods for the enzymic characterization of Latin-American Leishmania with particular reference to Leishmania mexicana amazonensis and subspecies of Leishmania hertigi

30 Brazilian stocks of Leishmania mexicana amazonensis and 13 stocks of subspecies of Leishmania hertigi were characterized by starch-gel electrophoresis, using 18 enzymes selected from a total of 36 investigated. L. m. amazonensis was separable from subspecies of L. hertigi by enzymic profiles of 11 enzymes. The L. m. amazonensis stocks, which were from a wide range of hosts in a large geographical area, were enzymically extremely homogeneous, and could only be subdivided on two enzymes; sub-groups did not relate to each other or to any differences in epidemiological characters, including the clinical form of the human disease. 12 stocks regarded as L. hertigi deanei, that were isolated from Coendou prehensilis prehensilis and Coendou sp. in Pará State, Brazil, were separable into two sub-groups by three enzymes. A single stock of L. hertigi hertigi from Panama was separable from both enzymic sub-groups of L. h. deanei, in each case by three enzymes. The significance of these and other characters of diversity is discussed, together with the use of enzymes for the identification of the leishmaniae.

Isoenzyme characterization of Leishmania species from Iraq

Leishmaniasis in Iraq takes both the visceral and cutaneous forms. The causative organisms are identified according to the electrophoretic variation of the enzymes MDH, GPI, 6PGD, PGM and IDH. The 37 visceral stocks investigated fall into two groups which differ only with respect to GPI. The six cutaneous stocks were divided into three groups. Group 3 represents Leishmania major, while groups 4 and 5 refer to L. tropica showing intraspecific variation with regard to 6PGD.

Evidence for NADH- and NADPH-linked glutamate dehydrogenases in Trypanosoma cruzi epimastigotes

Two glutamate dehydrogenases, NADH-linked (EC 1.2.1.2) and NADPH-linked (EC 1.2.1.4) were isolated from the epimastigote forms of Trypanosoma cruzi and purified. Both enzymes exist as hexamers. The molecular weights of the native NADH-and NADPH-linked glutamate dehydrogenases were estimated to be 360,000 and 265,000, respectively, and those of the subunits to be 58,000 and 43,000, respectively. The isoelectric point of the NADH-linked dehydrogenase is at pH 5.25 and that of the NADPH-linked enzyme at pH 5.1. The activities of both enzymes are regulated by product inhibition. In addition, purine nucleotides were shown to be potent inhibitors of the NADH-linked glutamate dehydrogenase.

Evidence for a functional glyoxylate cycle in the leishmaniae

Isocitrate lyase (EC 4.1.3.1) and malate synthase (EC 4.1.3.2), the two enzymes characteristic of the glyoxylate cycle, were demonstrated in promastigotes of five species of Leishmania (L. brasiliensis, L. donovani, L. mexicana, L. tarentolae, and L. tropica). Both enzymes were present in cells grown in a medium containing 10 mM glucose. Substitution of glucose with 20 mM acetate did not enhance enzyme levels. Acetate was readily taken up and metabolized by the cells. The distribution of label from acetate into various intermediary metabolites indicates a functional glyoxylate cycle and its role in gluconeogenesis/glyconeogenesis. The glyoxylate cycle in conjunction with alanine-glyoxylate aminotransferase and glyoxylate-aspartate aminotransferase could also be important in providing glyoxylate, the precursor for glycine biosynthesis.

Identification of Leishmania spp. by radiorespirometry

Preliminary investigation of the application of radiorespirometric technic to protozoan parasites of man indicates a potential for rapid identification. This technic, developed for identification of bacteria, was modified for use with culture forms of Leishmania. Five strains of Leishmania were compared: 2 of L. donovani, 2S and K; L. brasilensis, 2936 and B; and 1 of L. tropica, A. Consisent and rapid (approximately 2 hr) identification was obtained by the radiorespirometric procedure. A computer-type analysis of the radiorespirometric profiles of the 5 strains permitted correct identification of each isolate at the strain level 100% of the time. This technic offers several advantages over many current procedures for identification of protozoan parasites: (A) It is simple, rapid and highly reproducible, (B) Since it does not rely on visual or spectrophotometric determination, it may be conducted in the presence of optically complex substances. (C) It requires relatively low numbers of organisms (approximately 2 x 10(5)/14C-labeled substrate). (D) It is based on differential enzymic activity between species and strains of organisms and therefore, ultimately, on inherent genetic determinates of the parasites. (E) Further development of the procedure and accumulation of a data reference "bank" would allow automation of most of the identification process.