Product distribution of arsenite methylation catalyzed by hAS3MT in different reductive systems. The reaction system containing hAS3MT (2.0 μm), reductant, AdoMet (1.0 mm), iAs3+ (1.0 μm), and phosphate buffer was incubated at 37 °C for different times. The concentrations of GSH, cysteine, and TCEP were 7, 10, and 0.7 mm, respectively. Values are presented as the means ± S.D. of three separate experiments. Error bars represent S.D. from the mean of three independent experiments.