Contribution of glucose transport to the control of the glycolytic flux in Trypanosoma brucei

Abstract

The rate of glucose transport across the plasma membrane of the bloodstream form of Trypanosoma brucei was modulated by titration of the hexose transporter with the inhibitor phloretin, and the effect on the glycolytic f lux was measured. A rapid glucose uptake assay was developed to measure the transport activity independently of the glycolytic f lux. Phloretin proved a competitive inhibitor. When the effect of the intracellular glucose concentration on the inhibition was taken into account, the f lux control coefficient of the glucose transporter was between 0.3 and 0.5 at 5 mM glucose. Because the f lux control coefficients of all steps in a metabolic pathway sum to 1, this result proves that glucose transport is not the rate-limiting step of trypanosome glycolysis. Under physiological conditions, transport shares the control with other steps. At glucose concentrations much lower than physiological, the glucose carrier assumed all control, in close agreement with model predictions.

Strategies to determine the extent of control exerted by glucose transport on glycolytic flux in the yeast Saccharomyces bayanus

“…Secondly, at constant concentration of the transporter enzyme(s), one can modulate the activity of glucose transport with specific effectors, a method which has successfully been applied to determine the metabolic control of the glucose transport step in the parasite causing sleeping sickness, Trypanosoma brucei (Bakker et al, 1999). Several specific inhibitors of glucose transport in cells of eukaryotes have been described.…”

Oleanonic acid from Lippia lupulina (Verbenaceae) shows strong in vitro antileishmanial and antitrypanosomal activity

“…Similar results were observed for sakuranetin (5) in our experiments against epimastigote forms of T. cruzi Y strain (IC 50 47.5 µg mL -1 , Table 2). Although the dihydrochalcone phloretin (4) did not show detectable trypanocidal activity in our work (IC 50 higher than 365 µM, Table 2), it has been described to influence the glucose metabolism of T. cruzi, T. brucei, and T. rangeli (Bakker et al 1999;Einicker-Lamas et al 2000;Miletti et al 2006). …”

Systems biology tools for toxicology

“…In such cases, the flux control might be 0.3 or 0.7. This has allowed the establishment of the pattern of flux control for a number of cases both directly and experimentally (Bakker et al 1999;Groen et al 1982a) and by an integration of experimental data into a model (Bakker et al 1999;Groen et al 1982a).…”

“…The strongest flux control resided in the glucose transport step. This led to the prediction that the glucose transporter is the best predicted drug target, rather than glyceraldehyde-3-phosphate dehydrogenase, which is the drug target that is mostly worked on (Bakker et al 1999). The next step is here to perform differential control analysis, which compares the flux through a single metabolic pathway in a pathogen and host, finding the control coefficients in both.…”