The biomethylation of arsenic

Hao Li
A semi-continuous hydride generation-gas chromatography-atomic absorption spectrometry (HG-GC-AA) system was developed and optimized for the determination of arsenite, arsenate, methylarsonate (MMA), dimethylarsinate (DMA), and trimethylarsine oxide (TMAO). Particularly, this system was used to study the pathway for the biomethylation of arsenicals in microorganisms and a marine alga. The HG-GC-AA system was used to separate and identify the extracellular arsenic metabolites produced by the
more » ... oorganisms Apiotrichum humicola (previously known as Candida humicola) and Scopulariopsis brevicaulis growing in the liquid medium enriched with arsenicals. Arsenite, MMA, DMA, and TMAO were detected following incubation with arsenate. With arsenite as a substrate, the metabolites were MMA, DMA, and TMAO; MMA afforded DMA and TMAO, and DMA afforded TMAO. Trimethylarsine was not detected in these investigations. The production of the anticipated methylated intermediates from the substrates strongly support the metabolic sequence proposed by Challenger (Challenger, F Chem. Rev., 1945, 36:315). When L3-methionine-methyl-d₃ was added to the growing culture of Apiotrichum humicola grown in the presence of either arsenate, arsenite, MMA, or DMA, the CD₃ label was incorporated intact into the arsenic metabolites (DMA and TMAO) to a considerable extent, indicating that S-adenosylmethionine (SAM), or some related suiphonium compound, is involved in the biological methylation. Conclusive evidence of CD₃ incorporation into the arsenicals was provided by using a specially developed hydride generation-gas chromatography-mass spectrometry methodology (HG-GC-MS). When a unicellular marine alga Polyphysa peniculus was grown in artificial seawater enriched with arsenicals, the arsenic metabolites produced in the cells as well as in the growth medium were identified by using HG-GC-AA methodology. Arsenite and DMA were detected following incubation with arsenate. When the alga was treated with arsenite, DMA was the m [...]
doi:10.14288/1.0059605 fatcat:tqhyez4kjjfsxhkalglqtcisey