Melatonin biosynthesis pathway (None (no standard abbreviation for the pathway itself; abbreviations exist for enzymes within the pathway, such as AANAT and ASMT))

The melatonin biosynthesis pathway, sometimes called the tryptophan–serotonin–melatonin metabolic cascade, describes a series of enzymatic reactions that convert L-tryptophan into serotonin and then into melatonin. This process occurs primarily in animals' pineal gland but also takes place in other tissues across plants and microorganisms. Key steps involve hydroxylation by tryptophan hydroxylase forming 5-hydroxytryptophan; decarboxylation by aromatic L-amino acid decarboxylase yielding serotonin; acetylation by serotonin N-acetyltransferase producing N-acetylserotonin; finally methylation by acetylserotonin O-methyltransferase generating melatonin. This hormone regulates circadian rhythms via action on G protein-coupled receptors MT1 and MT2 but also acts as an antioxidant protecting cells from oxidative damage. Dysregulation has been implicated in mood disorders such as depression.

Other names

Melatonin synthesis pathwayMelatonin production pathwayTryptophan–serotonin–melatonin metabolic cascade

Not applicable to the whole "pathway." For individual enzymes: - Inhibition or activation of key synthetic enzymes alters endogenous melatonin levels. - Drugs may act as agonists at downstream receptors after synthesis is complete.