Purified CmArsM is a thermophylic arsenite S-adenosylmethionine methyltransferase. (A) The products of methylation by 2.2 μM purified CmArsM7 and CmArsM8 at 37 °C were analyzed by HPLC-ICP-MS, with instrumental output in arbitrary units. (B) The products of methylation by 3 μM CmArsM7 were examined as a function of assay temperature after 30 min. From left to right the 4 bars at each temperature are: starting amount of As(III), As(III), MMAs(III), and DMAs(V). (C) Arsenic methylation was assayed with 1.5 μM CmArsM7 and analyzed by HPLC-ICP-MS: ●, As(III); ▼, MMAs(III); ○, DMAs(V). The error bars indicate the standard error of 3 assays. Curves are displaced on the y axis for clarity.