ARSENIC BIOMETHYLATION BY THE MICROORGANISM APIOTRICHUM HUMICOLA IN THE PRESENCE OF L-METHIONINE-METHYL-D(3)

The microorganism Apiotrichum humicola (previously known as Candida hu micola) grown in the presence of either arsenate, arsenite, methyl-ars onic acid or dimethylarsinic acid, produces arsenic-containing metabol ites in the growth medium. When L-methionine-methyl-d(3) is added to t he cultures, the CD3 label is incorporated intact into the metabolites to a considerable extent to form deuterated dimethylarsenic and trime thylarsenic species, indicating that S-adenosylmethionine, or some rel ated sulphonium compound, is involved in the biological methylation. C onclusive evidence of CD3 incorporation in the arsenicals found in the growth medium was provided by using a specially developed hydride gen eration-gas chromatography-mass spectrometry system (HG-GC-MS).