TRYPANOTHIONE-DEPENDENT PEROXIDE METABOLISM IN TRYPANOSOMA-CRUZI DIFFERENT STAGES

Different stages of Trypanosoma cruzi are able to metabolize low concentrations of H2O2. Trypomastigotes showed a higher initial rate per mg protein than amastigotes or epimastigotes derived from them. Amastigotes could metabolize H2O2 at a lower rate than the other developmental stages of T. cruzi. A peroxide-metabolizing activity was detected in extracts of T. cruzi epimastigotes. This 'NADPH peroxidase' activity was lost upon dialysis of the extracts and was probably due to a nonenzymatic reaction(s) with endogenous dihydrotrypanothione (T(SH)2) and/or other thiols, thus explaining the inhibition of H2O2 metabolism in intact cells by thiol inhibitors. An amount of non-protein thiols equivalent to an intracellular concentration of 2.0-3.0 mM was found in epimastigotes, which is sufficient to account for the rate of NADPH oxidation observed in the presence of high concentration of peroxides (> 100 muM). Addition of T(SH)2 increased this rate, implying that this thiol could be used as a substrate in that reaction. In addition, this activity was hardly detectable in the extracts in the presence of low concentration of peroxides (<20 muM), indicating a high K(m), which would be incompatible with a true peroxidase activity. Taking into account the high intracellular concentration of thiols measured, this activity probably accounted for the rates of H2O2 metabolism detected in intact T. cruzi. These results also confirm that T. cruzi is an organism with limited ability to detoxify H2O2.