Fig. 1. Biotransformation process of arsenic in the human body. 1. Inorganic arsenic compounds are actively transported into cells by a transporter. The transported arsenate (As^V) would also be reduced to arsenite (As^III) by arsenate reductase and glutathione (GSH). 2. As^III is methylated by arsenic methyltransferase (AS₃MT) to form monomethylarsonic acid (MMA^V) with the methyl group donor (S-adenosylmethionine, SAM). 3. MMA^V reductase reduces MMA^V to monomethylarsonous acid (MMA^III). Following the MMA^III methylated with AS₃MT, it was reduced to dimethlyarsinic acid (DMA^III).