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Trypanosomatids differ from. ail other organisms in their abirity to conJugare the-sulfur-containing tripeptide, glutathio-ne, and the poryaminJ, spermioine, to form trypanothione 1Nr, N8-bis (grurathionyr) spermiainel. i" g. ri"", with the NADPH-dependent flavoprotein, trypanothione reductase, the dithior form of trypanothione provides an intraceilurar reducing environment in tror. purusites, substituting for glutathione and glutathione reductase found in the mammalian host. Trypanothione and iti rerated enzymes* e-liuotueu in defense against damage by oxidants, certain heavy metalr, un. possibly xenobiotics. Trypanothione and its metaboric precursor, grutathionyrspermidr] le'ar: also implicated in the moduration of spermidine rivers d;;; growrh. several. existing trypanocidar drugs interact with the trypanothione sysrem, suggesting that rrypanothione metabolism rnay ue a good turgei ror tte development of new. drugs. The purification and properties of three key enzymes (grutathionyrspermidine synthetase, trypanothione synthetase, and trypanothione reductase) are discussed, and the-catalytic mechanism, sub_ strate-specificity, and the three-dimensionar structure oi trypanothione reduc_ tase are compared to that of glutathione reductase.