Arsenite methyltransferase (AS3MT)

Arsenite methyltransferase (AS3MT) is an S-adenosylmethionine-dependent enzyme that catalyzes the transfer of methyl groups to inorganic arsenic (As(III)), converting it into mono- and dimethylated arsenicals as part of the body's arsenic detoxification pathway[1][2][3]. The enzyme is primarily expressed in the liver and is crucial for biotransformation of arsenic compounds: the initial substrate (inorganic arsenite) is sequentially methylated to monomethylarsonic acid (MAs) and dimethylarsinic acid (DMAs). While this methylation generally increases urinary excretion and lowers toxicity, certain methylated trivalent intermediates are more toxic and carcinogenic than the parent inorganic arsenic. AS3MT's function is central to arsenic metabolism, modulating individual susceptibility to arsenic poisoning, cancer, and related health effects. The enzyme's activity relies on conserved cysteine residues for catalysis and uses thioredoxin and reduced glutathione as reductants in the methylation cycle[1][2][3]. Genetic variation in human AS3MT affects arsenic metabolism efficiency and can influence disease risk following arsenic exposure.

Other names

S-adenosyl-L-methionine:arsenic(III) methyltransferaseMethylarsonite methyltransferaseS-adenosylmethionine:arsenic (III) methyltransferaseArsenic (+3 oxidation state) methyltransferaseMethyltransferase CYT19CYT19

Catalyzes the transfer of methyl groups from S-adenosylmethionine (SAM) to arsenic(III) compounds, transforming inorganic arsenic into mono- and dimethylated arsenicals[1][2].