TRYPANOTHIONE-DEPENDENT PEROXIDE METABOLISM IN TRYPANOSOMA-CRUZI DIFFERENT STAGES

Different stages of Trypanosoma cruzi are able to metabolize low conce ntrations of H2O2. Trypomastigotes showed a higher initial rate per mg protein than amastigotes or epimastigotes derived from them. Amastigo tes 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 w as lost upon dialysis of the extracts and was probably due to a nonenz ymatic reaction(s) with endogenous dihydrotrypanothione (T(SH)2) and/o r other thiols, thus explaining the inhibition of H2O2 metabolism in i ntact cells by thiol inhibitors. An amount of non-protein thiols equiv alent to an intracellular concentration of 2.0-3.0 mM was found in epi mastigotes, which is sufficient to account for the rate of NADPH oxida tion observed in the presence of high concentration of peroxides (> 10 0 muM). Addition of T(SH)2 increased this rate, implying that this thi ol could be used as a substrate in that reaction. In addition, this ac tivity was hardly detectable in the extracts in the presence of low co ncentration of peroxides (<20 muM), indicating a high K(m), which woul d be incompatible with a true peroxidase activity. Taking into account the high intracellular concentration of thiols measured, this activit y probably accounted for the rates of H2O2 metabolism detected in inta ct T. cruzi. These results also confirm that T. cruzi is an organism w ith limited ability to detoxify H2O2.