Thiopurine S‑methyltransferase- and indolethylamine N‑methyltransferase-mediated formation of methylated tellurium compounds from tellurite

Tellurium (Te) is a metalloid widely used in various industries. However, its toxicological impact on humans is poorly understood. In this study, we investigated the role of two methyltransferases, thiopurine S‑methyltransferase (TPMT) and indolethylamine N‑methyltransferase (INMT), in the methylation of tellurite, an inorganic Te oxyanion. The products of the reaction of Te compounds catalyzed by recombinant human TPMT and/or INMT were analyzed by liquid chromatography hyphenated to inductively coupled plasma mass spectrometry (LC-ICP-MS) and gas chromatography mass spectrometry (GC-MS). We found that TPMT catalyzes the methylation of non-methylated Te and methanetellurol to generate dimethyltelluride. On the other hand, INMT catalyzes the methylation of methanetellurol and dimethyltelluride to produce trimethyltelluronium ion, a metabolite excreted into animal urine. We conclude that TPMT and INMT are cooperatively responsible for the detoxification of Te oxyanions through methylation to form trimethyltelluronium ions.