Hysteresis of pyruvate phosphate dikinase from Trypanosoma cruzi.

Trypanosoma cruzi, the causative agent of Chagas' disease, belongs to the Trypanosomatidae family. The parasite undergoes multiple morphological and metabolic changes during its life cycle, in which it can use both glucose and amino acids as carbon and energy sources. The glycolytic pathway is peculiar in that its first six or seven steps are compartmentalized in glycosomes, and has a two-branched auxiliary glycosomal system functioning beyond the intermediate phosphoenolpyruvate (PEP) that is also used in the cytosol as substrate by pyruvate kinase. The pyruvate phosphate dikinase (PPDK) is the first enzyme of one branch, converting PEP, PPi, and AMP into pyruvate, Pi, and ATP. Here we present a kinetic study of PPDK from T. cruzi that reveals its hysteretic behavior. The length of the lag phase, and therefore the time for reaching higher specific activity values is affected by the concentration of the enzyme, the presence of hydrogen ions and the concentrations of the enzyme's substrates. Additionally, the formation of a more active PPDK with more complex structure is promoted by it substrates and the cation ammonium, indicating that this enzyme equilibrates between the monomeric (less active) and a more complex (more active) form depending on the medium. These results confirm the hysteretic behavior of PPDK and are suggestive for its functioning as a regulatory mechanism of this auxiliary pathway. Such a regulation could serve to distribute the glycolytic flux over the two auxiliary branches as a response to the different environments that the parasite encounters during its life cycle.