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ENZYME entry: EC 2.1.1.137

Accepted Name
arsenite methyltransferase.
Alternative Name(s)
methylarsonite methyltransferase.
Reaction catalysed
  • [thioredoxin]-dithiol + arsenic triglutathione + 2 H2O + S-adenosyl-L-methionine <=> [thioredoxin]-disulfide + 3 glutathione + H(+) + methylarsonous acid + S-adenosyl-L-homocysteine
  • 2 [thioredoxin]-dithiol + arsenic triglutathione + H2O + 2 S-adenosyl-L-methionine <=> 2 [thioredoxin]-disulfide + dimethylarsinous acid + 3 glutathione + 2 H(+) + 2 S-adenosyl-L-homocysteine
  • 3 [thioredoxin]-dithiol + arsenic triglutathione + 3 S-adenosyl-L-methionine <=> 3 [thioredoxin]-disulfide + 3 glutathione + 3 H(+) + 3 S-adenosyl-L-homocysteine + trimethylarsine
Comment(s)
  • An enzyme responsible for synthesis of trivalent methylarsenical antibiotics in microbes or detoxification of inorganic arsenous acid in animals.
  • The in vivo substrate is arsenic triglutathione or similar thiol (depending on the organism), from which the arsenic is transferred to the enzyme forming bonds with the thiol groups of three cysteine residues via a disulfide bond cascade pathway.
  • Most of the substrates undergo two methylations and are converted to dimethylarsinous acid.
  • However, a small fraction are released earlier as methylarsonous acid, and a smaller amount proceeds via a third methylation, resulting in the volatile product trimethylarsane.
  • Methylation involves temporary oxidation to arsenic(V) valency, followed by reduction back to arsenic(III) valency using electrons provided by thioredoxin or a similar reduction system.
  • The arsenic(III) products are quickly oxidized in the presence of oxygen to the corresponding arsenic(V) species.
Cross-references
BRENDA2.1.1.137
EC2PDB2.1.1.137
ExplorEnz2.1.1.137
PRIAM enzyme-specific profiles2.1.1.137
KEGG Ligand Database for Enzyme Nomenclature2.1.1.137
IUBMB Enzyme Nomenclature2.1.1.137
IntEnz2.1.1.137
MEDLINEFind literature relating to 2.1.1.137
MetaCyc2.1.1.137
Rhea expert-curated reactions2.1.1.137
UniProtKB/Swiss-Prot
A0A0D3MJQ5, ARSM_CLOSP;  O52025, ARSM_HALSA;  Q8TJK1, ARSM_METAC;  
U2ZU49, ARSM_PSEA4;  Q6N3Y0, ARSM_RHOPA;  Q9HBK9, AS3MT_HUMAN;  
Q91WU5, AS3MT_MOUSE;  Q8VHT6, AS3MT_RAT;  

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