title: Melatonin and its metabolites: new findings regarding their production and their radical scavenging actions.
abstract: This review summarizes some of the recent findings concerning the long-held tenet that the enzyme, N-acetyltransferase, which is involved in the production of N-acetylserotonin, the immediate precursor of melatonin, may in fact not always control the quantity of melatonin generated. New evidence from several different laboratories indicates that hydroxyindole-O-methyltransferase, which O-methylates N-acetylserotonin to melatonin may be rate-limiting in some cases. Also, the review makes the point that melatonin's actions are uncommonly widespread in organs due to the fact that it works via membrane receptors, nuclear receptors/binding sites and receptor-independent mechanisms, i.e., the direct scavenging of free radicals. Finally, the review briefly summarizes the actions of melatonin and its metabolites in the detoxification of oxygen and nitrogen-based free radicals and related non-radical products. Via these multiple processes, melatonin is capable of influencing the metabolism of every cell in the organism.
authors.affiliation: Department of Cellular and Structural Biology, University of Texas Health Science Center at San Antonio, San Antonio 78229-3900, USA. reiter@uthscsa.edu
authors.forename: Russel J
authors.initials: RJ
authors.lastname: Reiter
authors.forename: Dun-xian
authors.initials: DX
authors.lastname: Tan
authors.forename: M Pilar
authors.initials: MP
authors.lastname: Terron
authors.forename: Luis J
authors.initials: LJ
authors.lastname: Flores
authors.forename: Zbigniew
authors.initials: Z
authors.lastname: Czarnocki
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000378:metabolism; D016166:Free Radical Scavengers / Q000378:metabolism*; D005978:Glutathione / Q000378:metabolism; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism; D017665:Hydroxyl Radical / Q000378:metabolism; D008550:Melatonin / Q000096:biosynthesis / Q000378:metabolism / Q000502:physiology*
chemical_list: D000975:Antioxidants; D016166:Free Radical Scavengers; D017665:Hydroxyl Radical; D006861:Hydrogen Peroxide; D005978:Glutathione; D008550:Melatonin