Investigations into the role of methylcobalamin and glutathione for the methylation of antimony using isotopically enriched antimony(V)

Glutathione (gamma-Glu-Cys-Gly, GSH) and methylcobalamin (CH3-B-12) may play a role in the biomethylation process of antimony. To understand better the transformation of antimony in biological systems, we studied abiotic and biomethylation processes and the influence of GSH in the methylation. CH3-B-12, acting as a possible methylating agent for antimony, was studied with GSH and in the absence of GSH. The most abundant product of this reaction was monomethylantimony, with a small concentration of the dimethylantimony species, as identified by hydride generation cryotrapping gas chromatography inductively coupled plasma mass spectrometry (HG-CT-GC-ICP-MS). In the same experiments we found that tris(gamma-Glu-Cys-Gly)trithioantimonite [Sb(GS)(3)] and di(gamma-Glu-Cys-Gly)methyldithioantimonite [(CH3)Sb(GS)(2)] complexes were present using flow-injection electrospray ionization MS. Both complexes were also identified in a fermented sewage sample, suggesting that these complexes may play a role as intermediates in the biomethylation of antimony. However, CH3-B-12 is not the sole methylation agent, since it does not produce any trimethylantimony species as identified in anaerobic sewage sludge cultures inoculated with enriched Sb-123(V). Species-specific Sb-123/121 isotope ratio measurements of the different methylantimony species suggest a stepwise methylation of antimony according to the Challenger mechanism. Copyright (C) 2004 John Wiley Sons, Ltd.