ASMT belongs to the methyltransferase superfamily and is involved in melatonin biosynthesis. Expressed in brain, retina and pineal gland, ASMT functions to catalyze the final reaction in the synthesis of melatonin, specifically the conversion of S-adenosyl-L-methionine and N-acetylserotonin to S-adenosyl-Lhomocysteine and melatonin.