title: Kinetic modeling can describe in vivo glycolysis in Entamoeba histolytica.
abstract: Glycolysis in the human parasite Entamoeba histolytica is characterized by the absence of cooperative modulation and the prevalence of pyrophosphate-dependent (over ATP-dependent) enzymes. To determine the flux-control distribution of glycolysis and understand its underlying control mechanisms, a kinetic model of the pathway was constructed by using the software gepasi. The model was based on the kinetic parameters determined in the purified recombinant enzymes, and the enzyme activities, and steady-state fluxes and metabolite concentrations determined in amoebal trophozoites. The model predicted, with a high degree of accuracy, the flux and metabolite concentrations found in trophozoites, but only when the pyrophosphate concentration was held constant; at variable pyrophosphate, the model was not able to completely account for the ATP production/consumption balance, indicating the importance of the pyrophosphate homeostasis for amoebal glycolysis. Control analysis by the model revealed that hexokinase exerted the highest flux control (73%), as a result of its low cellular activity and strong AMP inhibition. 3-Phosphoglycerate mutase also exhibited significant flux control (65%) whereas the other pathway enzymes showed little or no control. The control of the ATP concentration was also mainly exerted by ATP consuming processes and 3-phosphoglycerate mutase and hexokinase (in the producing block). The model also indicated that, in order to diminish the amoebal glycolytic flux by 50%, it was required to decrease hexokinase or 3-phosphoglycerate mutase by 24% and 55%, respectively, or by 18% for both enzymes. By contrast, to attain the same reduction in flux by inhibiting the pyrophosphate-dependent enzymes pyrophosphate-phosphofructokinase and pyruvate phosphate dikinase, they should be decreased > 70%. On the basis of metabolic control analysis, steps whose inhibition would have stronger negative effects on the energy metabolism of this parasite were identified, thus becoming alternative targets for drug design.
authors.affiliation: Departamento de Bioquímica, Instituto Nacional de Cardiología, México DF, México. emma_saavedra2002@yahoo.com
authors.forename: Emma
authors.initials: E
authors.lastname: Saavedra
authors.forename: Alvaro
authors.initials: A
authors.lastname: Marín-Hernández
authors.forename: Rusely
authors.initials: R
authors.lastname: Encalada
authors.forename: Alfonso
authors.initials: A
authors.lastname: Olivos
authors.forename: Guillermo
authors.initials: G
authors.lastname: Mendoza-Hernández
authors.forename: Rafael
authors.initials: R
authors.lastname: Moreno-Sánchez
mesh_terms: D000818:Animals; D004748:Entamoeba histolytica / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D004749:Entamoebiasis / Q000188:drug therapy; D000431:Ethanol / Q000378:metabolism; D006019:Glycolysis / Q000187:drug effects; D006593:Hexokinase / Q000378:metabolism; D007700:Kinetics; D008954:Models, Biological; D013997:Time Factors; D017186:Titrimetry