N-Acetylserotonin O-methyltransferase, also known as ASMT, is an enzyme which catalyzes the final reaction in melatonin biosynthesis: converting Normelatonin to melatonin. This reaction is embedded in the more general tryptophan metabolism pathway. The enzyme also catalyzes a second reaction in tryptophan metabolism: the conversion of 5-hydroxy-indoleacetate to 5-methoxy-indoleacetate. The other enzyme which catalyzes this reaction is n-acetylserotonin-o-methyltransferase-like-protein.
In humans the ASMT enzyme is encoded by the pseudoautosomal ASMT gene. A copy exists near the endcaps of the short arms of both the X chromosome and the Y chromosome.
