Abstract
Demonstrating the enzymatic basis of arsenic methylation is critical to further studies of the pathway for the conversion of inorganic arsenic into a variety of methylated metabolites. This protocol describes a procedure for the purification of an arsenic methyltransferase from rat liver cytosol. Purification of this enzyme and subsequent cloning of its gene has permitted studies of enzyme structure and function, and has lead to the identification of orthologous genes in genomes of organisms ranging in complexity from sea urchins to humans. These proteins are referred to as arsenic (+3 oxidation state) methyltransferases.