Studies on the metabolism of the protozoa. 7. Comparative carbohydrate metabolism of eleven species of trypanosome

Ryley, J. F.

doi:10.1042/bj0620215

Cited by 170 publications

(52 citation statements)

References 13 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…3). Under aerobic conditions, bloodstream-form trypanosomes convert all glucose to pyruvate, with the concomitant consumption of one molecule of oxygen per molecule of glucose (33). Therefore, the rate of oxygen consumption is a measure of the steady-state glycolytic flux.…”

Section: Resultsmentioning

confidence: 99%

“…Because phloretin competed with glucose, the inhibition of the transporter depended on the actual glucose concentration. The glucose concentration was measured at the start of the experiment, and the actual concentration at the moment of addition of the inhibitor was calculated based on the fact that trypanosomes consume one molecule of glucose per molecule of oxygen (33).…”

Section: Chemicals D-[u-mentioning

confidence: 99%

See 1 more Smart Citation

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

Bakker

Walsh

Kuile

et al. 1999

Proc. Natl. Acad. Sci. U.S.A.

View full text Add to dashboard Cite

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.

show abstract

Section: Resultsmentioning

confidence: 99%

Section: Chemicals D-[u-mentioning

confidence: 99%

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

Bakker

Walsh

Kuile

et al. 1999

Proc. Natl. Acad. Sci. U.S.A.

View full text Add to dashboard Cite

show abstract

“…The lethality for BF T. brucei upon KREN3 repression is puzzling since normal BFs, which rely on glycolysis, have less edited COII mRNA than PFs (2,14,15) and lack cytochrome c oxidase (complex IV) activity (16,44,51,52). Indeed, BF cytochrome c oxidase subunit 6 null mutants are viable (60).…”

Section: Discussionmentioning

confidence: 99%

RNA Editing in Trypanosoma brucei Requires Three Different Editosomes

Carnes

Trotter

Peltan

et al. 2008

Molecular and Cellular Biology

106

150

View full text Add to dashboard Cite

Trypanosoma brucei has three distinct ϳ20S editosomes that catalyze RNA editing by the insertion and deletion of uridylates. Editosomes with the KREN1 or KREN2 RNase III type endonucleases specifically cleave deletion and insertion editing site substrates, respectively. We report here that editosomes with KREPB2, which also has an RNase III motif, specifically cleave cytochrome oxidase II (COII) pre-mRNA insertion editing site substrates in vitro. Conditional repression and mutation studies also show that KREPB2 is an editing endonuclease specifically required for COII mRNA editing in vivo. Furthermore, KREPB2 expression is essential for the growth and survival of bloodstream forms. Thus, editing in T. brucei requires at least three compositionally and functionally distinct ϳ20S editosomes, two of which distinguish between different insertion editing sites. This unexpected finding reveals an additional level of complexity in the RNA editing process and suggests a mechanism for how the selection of sites for editing in vivo is controlled.RNA editing recodes most of the mitochondrial mRNAs in trypanosomatids by the insertion and deletion of uridine nucleotides (U's) using information provided by guide RNAs (gRNAs) (58). RNA editing is developmentally regulated and is required for parasites that cycle between insect vector and mammalian host (54). Proteins that perform catalytic steps of RNA editing have been identified: endonucleases KREN1 or KREN2 cleave at deletion or insertion sites, respectively; terminal uridylyl transferase (TUTase) KRET2 adds U's at insertion sites; U specific exoribonuclease (exoUase) KREX1 removes U's at deletion sites; and ligases KREL1 or KREL2 rejoin mRNA fragments after U addition or removal (5,13,25,30,34,55,61). These catalytic steps are coordinated by the multiprotein editosomes that sediment at ϳ20S on glycerol gradients (9, 43). KREPB2 was identified as an editosome component by mass spectrometry, and found to contain an RNase III motif harboring amino acids that are critical for catalysis, a U1 Zn 2ϩ finger, and double-stranded RNA binding. It has sequence similarity to KREN1 and KREN2, which also contain these three motifs (23,41,64). These data strongly suggest an RNA editing endonuclease role for KREPB2.KREN1 and KREN2 were shown to be RNA editing endonucleases using both RNA interference (RNAi) and conditional knockout cell lines (5, 61). Both KREN1 and KREN2 are essential for the normal growth of PF and BF cells, and repression of their expression by either method led to dramatic growth defects or death, respectively. Such repression of KREN1 eliminated in vitro cleavage by ϳ20S editosomes of a deletion site in a synthetic substrate modeled on ATPase subunit 6 (A6) pre-mRNA but did not alter cleavage of an insertion site in a substrate derived from the same mRNA. These studies and other data have shown that KREN1 is an editing endonuclease with a preference for sites from which U's are deleted (29). Similarly, repression of KREN2 eliminated in vitro cleavage at insertion ed...

show abstract

“…In these trypanosomes lactate dehydrogenase is absent [l] and NADH generated in glycolysis is re-oxidized indirectly by molecular oxygen via a dihydroxyacetone phosphate : glycerol-3-phosphate shuttle in which the enzymes glycerol-3-phosphate oxidase and NAD + -linked glycerol-3-phosphate dehydrogenase are involved [2]. Under aerobic conditions, glucose cannot be oxidized beyond pyruvate, which appears to be the exclusive end-product of glycolysis [3,4], whereas under anaerobic conditions equimolar amounts of pyruvate and glycerol are excreted [3,5]. This anaerobic dis-624 Glycolysis in Trypanosoma brucei mutation of glucose, which can be mimicked by incubating trypanosomes in the presence of 1 mM salicylhydroxamic acid [6,7] proceeds with net ATP synthesis [7], an observation which cannot readily be explained from the data available at present.…”

mentioning

confidence: 99%

Glycolysis in Trypanosoma brucei

Visser

Opperdoes

1980

European Journal of Biochemistry

122

View full text Add to dashboard Cite

The possibility that the glycosomes present in the bloodstream form of Trypanosoma brucei FEBS Lett. 80, 360-3641 constitute a separate pool of glycolytic intermediates within the cell was investigated.In titrations of intact cells with digitonin, a differential activation of glycolytic enzymes was observed. Enolase, pyruvate kinase and the cell-sap marker alanine aminotransferase were activated at 0.05 mg digitonin per mg protein. The nine glycosomal enzymes involved in the conversion of glucose and glycerol into 3-phosphoglycerate were activated only at digitonin concentrations between 0.7 and 9.8 mg/mg protein. In subcellular fractions the activities or the latter enzymes were all latent between 70 and 92 %. Latency was abolished by addition of 0.1 % Triton X-100 or partly by five cycles of freezing and thawing. We conclude that the glycosomal enzymes are surrounded by a membrane, which forms a permeability barrier to intermediates and co-factors of glycolysis.The concentrations of glycolytic intermediates and of adenine nucleotides were measured under aerobic conditions as well as in the presence of 1 mM salicylhydroxamic acid, a respiratory inhibitor. Addition of salicylhydroxamic acid caused the following changes : (a) The levels of almost all glycolytic intermediates measured decreased. Glycerol-3-phosphate, however, increased fourfold. From the high levels of metabolite concentrations found and from comparison of the apparent mass-action ratios calculated for the separate glycolytic reactions with those for other organisms, we conclude that in bloodstream form T. brucei the glycolytic intermediates are present in the glycosomes as well as in the cytosol and that the two pools of intermediates equilibrate with each other, despite the presence of the glycosomal membrane.Bloodstream forms of the African trypanosomes belonging to the brucei group, like Trypanosoma brucei, Trypanosoma rhodesiense and Trypanosoma gambiense, are the causative agents of nagana in domestic animals Abbreviations. Dihydroxyacetone-P, dihydroxyacetone phosphate ; glycerol-3-P, sn-glycerol-3-phosphate; glycerate-3-P, 3-phosphoglycerate; glucose-6-P, glucose-6-phosphate; fructose-6-P, fructose-6-phosphate; fructose-l,h-Pz, fructose-1,6-bisphosphate; glycerate-2-P, 2-phosphoglycerate; glyceraldehyde-3-P, D-glyceraldehyde-3-phosphate.Enzymes. Hexokinase (EC 2.7.1.1); phosphoglucose isomerase (EC 5.3.1.9); 6-phosphofructokinase (EC 2.7.1.11); fructose-bisphosphate aldolase (EC 4.1.2.13); triosephosphate isomerase (EC 5.3.1 .l): sn-glycerol-3-phosphate dehydrogenase (EC 1.1.1.8); glycerol kinase (EC 2.7.1.30); glyceraldehyde-phosphate dehydrogenase (EC 1.2.1.12); phosphoglycerate kinase (EC 2.7.2.3); phosphoglyceromutase (EC 2.7.5.3); enolase (EC 4.2.1.11); pyruvate kinase (EC 2.7.1.40); alanine aminotransferase (EC 2.6.1.2). and live-stock and of the acute and chronic forms of sleeping sickness in man. For their energy needs, these organisms are entirely dependent on glycolysis which proceeds at an extremely high rate and differs in its...

show abstract

Studies on the metabolism of the protozoa. 7. Comparative carbohydrate metabolism of eleven species of trypanosome

Cited by 170 publications

References 13 publications

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

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

RNA Editing in Trypanosoma brucei Requires Three Different Editosomes

Glycolysis in Trypanosoma brucei

Contact Info

Product

Resources

About