Pyruvate phosphate dikinase and pyrophosphate metabolism in the glycosome of Trypanosoma cruzi epimastigotes.
Pyruvate phosphate dikinase (PPDK) was recently reported in trypanosomatids, but its metabolic function is not yet known. The present work deals with the cellular localization and the function of the Trypanosoma cruzi enzyme. First, we show by digitonin titration and cell fractionation that the enzyme was essentially present in the glycosome matrix of the epimastigote form. Second, we address the issue of the direction of the reaction inside the glycosome for one part, our bibliographic survey evidenced a quite exergonic DeltaGo' (at least -5.2 kcal/mol at neutral pH and physiologic ionic strength); for another part, no pyrophosphatase (PPase) could be detected in fractions corresponding to the glycosomes; therefore, glycosomal PPDK likely works in the direction of pyruvate production. Third, we address the issue of the origin of the glycosomal pyrophosphate (PPi): several synthetic pathways known to produce PPi are already considered to be glycosomal. This work also indicates the presence of an NADP(+)-dependent beta-oxidation of palmitoyl-CoA in the glycosome. Several pyruvate-consuming activities, in particular alanine dehydrogenase (ADH) and pyruvate carboxylase (PC), were detected in the glycosomal fraction. PPDK appears therefore as a central enzyme in the metabolism of the glycosome of T. cruzi by providing a link between glycolysis, fatty acid oxidation and biosynthetic PPi-producing pathways. Indeed, PPDK seems to replace pyrophosphatase in its classical thermodynamic role of displacing the equilibrium of PPi-producing reactions, as well as in its role of eliminating the toxic PPi.
Unidad de Bioquímica de Parásitos, Centro de Ingeniería Genética, Facultad de Ciencias, Universidad de Los Andes, Mérida 5101, Venezuela.
Héctor
H
Acosta
Michel
M
Dubourdieu
Wilfredo
W
Quiñones
Ana
A
Cáceres
Frederic
F
Bringaud
Juan Luis
JL
Concepción
D050788:Alanine Dehydrogenase; D000594:Amino Acid Oxidoreductases / Q000737:chemistry; D000818:Animals; D015153:Blotting, Western; D002254:Carbonates / Q000737:chemistry; D003902:Detergents / Q000494:pharmacology; D004072:Digitonin / Q000737:chemistry; D011756:Diphosphates / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D005227:Fatty Acids / Q000378:metabolism; D006019:Glycolysis; D006863:Hydrogen-Ion Concentration; D007477:Ions; D008830:Microbodies / Q000378:metabolism*; D008954:Models, Biological; D009249:NADP / Q000737:chemistry; D017830:Octoxynol; D010100:Oxygen / Q000378:metabolism; D011092:Polyethylene Glycols / Q000494:pharmacology; D011766:Pyruvate Carboxylase / Q000737:chemistry; D011772:Pyruvate, Orthophosphate Dikinase / Q000378:metabolism*; D011773:Pyruvates / Q000737:chemistry; D013347:Subcellular Fractions / Q000378:metabolism; D013816:Thermodynamics; D014349:Trypanosoma cruzi / Q000378:metabolism*
D002254:Carbonates; D003902:Detergents; D011756:Diphosphates; D005227:Fatty Acids; D007477:Ions; D011773:Pyruvates; D011092:Polyethylene Glycols; D009249:NADP; D017830:Octoxynol; C010615:Nonidet P-40; D000594:Amino Acid Oxidoreductases; D050788:Alanine Dehydrogenase; D011772:Pyruvate, Orthophosphate Dikinase; D011766:Pyruvate Carboxylase; D004072:Digitonin; D010100:Oxygen