CONICET | Buscador de Institutos y Recursos Humanos

The components of the redox metabolism in Entamoeba histolytica have beenrecently revisited by Arias et al. (Free Radic. Biol. Med. 42:1496-1505; 2007),after the identification and characterization of a thioredoxin-linked system. Thepresent work deals with studies performed for a better understanding of thelocalization and identification of different components of the redox machinerypresent in the parasite. The gene encoding for amoebic thioredoxin 8 was clonedand the recombinant protein typified as having properties similar to those ofthioredoxin 41. The ability of these thioredoxins and the specific reductase toassemble a system utilizing NADPH to metabolize hydroperoxides in associationwith a peroxiredoxin has been kinetically characterized. The peroxiredoxinbehaved as a typical 2 cysteine enzyme, exhibiting a ping-pong mechanism withhyperbolic saturation kinetics for thioredoxin 8 (K(m)=3.8 muM), thioredoxin 41(K(m)=3.1 muM), and tert-butyl hydroperoxide (K(m) about 35 muM). Moreover, thetandem system involving thioredoxin reductase and either thioredoxin proved to beoperative for reducing low molecular weight disulfides, including putativephysiological substrates as cystine and oxidized trypanothione. Thioredoxinreductase and thioredoxin 41 (by association also the functional redox system)have been immunolocalized underlying the plasma membrane in Entamoeba histolyticacells. These findings suggest an important role for the metabolic pathwayinvolving thioredoxin as a redox interchanger, which could be critical for themaintenance and virulence of the parasite when exposed to highly toxic reactiveoxygen species.