Arsenic Methyltransferase（AS3MT) catalyzes the transfer of a methyl group from S-adenosyl-L-methionine（AdoMet) to trivalent arsenical and may have a role in arsenic metabolism. AS3MT methylates arsenite to produce methylarsonate， Me-AsO3H2， which is reduced by methylarsonate reductase to methylarsonite， Me-As（OH)2. Methylarsonite which is also a substrate， is transformed into the much less toxic complex dimethylarsinate（cacodylate)， Me2As（O)-OH.
