Deficient metabolic utilization of hydrogen peroxide in Trypanosoma cruzi

Publisher Website
Google Scholar
Abstract
The glutathione peroxidase-glutathione reductase system, an alternative pathway for metabolic utilization of H2O2 was investigated in T. cruzi, an organism lacking catalase and deficient in peroxidase. The presence of glutathione (4.9 .+-. 0.7 nmol of reduced glutathione/108 cells) and NADPH-dependent glutathione reductase (5.3 .+-. 0.4 munit/108 cells) was demonstrated in the cytosolic fraction of the parasite, but with H2O2 as substrate glutathione peroxidase activity could not be demonstrated in the same extracts. With t-butyl hydroperoxide or cumene hydroperoxide as substrate, a very low NADPH-dependent glutathione peroxidase activity was detected (equivalent to 0.3-0.5 munit of peroxidase/108 cells, or about 10% of glutathione reductase activity). Blank reactions of the glutathione peroxidase assay (non-enzymic oxidation of glutathione by hydroperoxides and enzymic oxidation of NADPH) hampered accurate measurement of peroxidase activity. The presence of superoxide dismutase and ascorbate peroxidase activity in, and the absence of catalase from, epimastigote extracts was confirmed. Ascorbate peroxidase activity was cyanide-sensitive and heat-labile, but no activity could be demonstrated with diaminobenzidine, pyrogallol or guaiacol as electron donor. T. cruzi epimastigotes probably lack an adequate enzyme defense against H2O2 and H2O2-related free radicals.