Purification and properties of phosphoglucose isomerases of Trypanosoma cruzi

Glucosephosphate isomerase (PGI; EC 5.3.1.9) of Trypanosoma cruzi epimastig otes was found in about the same proportion in the glycosome and the cytoso l. This subcellular distribution is similar to that of Leishmania mexicana, but contrasts with that of T. brucei bloodstream form, where the enzyme is essentially restricted to the glycosome. Glucosephosphate isomerase was hi ghly purified from a glycosome-enriched fraction and to about 70% purity fr om the soluble extract. Both enzymes displayed Michaelis-Menten-Henri kinet ics. K-m values for fructose 6-phosphate were 0.125 +/- 0.07 and 0.80 +/- 0 .10 mM for the glycosomal and the cytosolic PGIs, respectively. Erythrose-4 -phosphate, 6-phosphogluconate and mannose-6-phosphate were inhibitors for both PGIs. Phosphogluconate and erythrose phosphate showed higher affinity for cytosolic PGI than for glycosomal PGI, by 2.5- and 4-fold respectively. The PGIs differed slightly in their isoelectric point (7.1 +/- 0.15 and 7. 5 +/- 0.12) and optimum pH range. Both PGIs also differed in their chromato graphic properties (ion-exchange and phenyl Sepharose), indicating a differ ence in charge and hydrophobicity, with the glycosomal enzyme being more hy drophobic. The molecular mass of both PGIs was 186/000 +/- 9000 Da, which i s higher than that of other known PGIs, including those from T. brucei and other trypanosomatids. The molecular mass of the subunit, 63 kDa, is simila r to that of PGIs from other sources. It appears that PGIs from T. cruzi ar e trimeric, in contrast with all other known PGIs which are dimeric. (C) 19 99 Elsevier Science Inc. All rights reserved.