The open reading frames of two different proteins with homologies to 2-Cys peroxiredoxins have been identified in the P. falciparum genome. Both genes, with a length of 585 and 648 bp, respectively, were amplified from a gametocyte cDNA and overexpressed in Escherichia coli. The gene products (deduced m 21.8 and 24.6 kDa) with an overall identity of 51.8% were found to be active in the glutamine synthetase protector assay. The smaller protein (named Pf-thioredoxin peroxidase 1; PfTPx1) is reduced by P. falciparum thioredoxin (PfTrx) and accepts H(2)O(2), t-butylhydroperoxide, and cumene hydroperoxide as substrates, the respective k(cat) values for the N-terminally His-tagged protein in the presence of 10 microM PfTrx and 200 microM substrate being 67, 56, and 41 min(-1) at 25 degrees C. As described for many peroxiredoxins, PfTPx1 does not follow saturation kinetics. Furthermore, in oxidizing milieu both proteins are converted to another protein species migrating faster in SDS gel electrophoresis. For PfTPx1 also this second species was found to be active, however, with different kinetic properties which might indicate a mechanism of enzyme regulation in vivo.