A Physiological Approach to Explore How Thioredoxin-Glutathione Reductase (TGR) and Peroxiredoxin (Prx) Eliminate H 2 O 2 in Cysticerci of Taenia .

Peroxiredoxins (Prxs) and glutathione peroxidases (GPxs) are the main enzymes of the thiol-dependent antioxidant systems responsible for reducing the H2 O2 produced via aerobic metabolism or parasitic organisms by the host organism. These antioxidant systems maintain a proper redox state in cells. The cysticerci of Taenia crassiceps tolerate millimolar concentrations of this oxidant. To understand the role played by Prxs in this cestode, two genes for Prxs, identified in the genome of Taenia solium ( Ts Prx1 and Ts Prx3), were cloned. The sequence of the proteins suggests that both isoforms belong to the class of typical Prxs 2-Cys. In addition, Ts Prx3 harbors a mitochondrial localization signal peptide and two motifs (-GGLG- and -YP-) associated with overoxidation. Our kinetic characterization assigns them as thioredoxin peroxidases (TPxs). While Ts Prx1 and Ts Prx3 exhibit the same catalytic efficiency, thioredoxin-glutathione reductase from T. crassiceps ( Tc TGR) was five and eight times higher. Additionally, the latter demonstrated a lower affinity (>30-fold) for H2 O2 in comparison with Ts Prx1 and Ts Prx3. The Tc TGR contains a Sec residue in its C-terminal, which confers additional peroxidase activity. The aforementioned aspect implies that Ts Prx1 and Ts Prx3 are catalytically active at low H2 O2 concentrations, and the Tc TGR acts at high H2 O2 concentrations. These results may explain why the T. crassiceps cysticerci can tolerate high H2 O2 concentrations.