title: Fundamental issues related to the origin of melatonin and melatonin isomers during evolution: relation to their biological functions.
abstract: Melatonin and melatonin isomers exist and/or coexist in living organisms including yeasts, bacteria and plants. The levels of melatonin isomers are significantly higher than that of melatonin in some plants and in several fermented products such as in wine and bread. Currently, there are no reports documenting the presence of melatonin isomers in vertebrates. From an evolutionary point of view, it is unlikely that melatonin isomers do not exist in vertebrates. On the other hand, large quantities of the microbial flora exist in the gut of the vertebrates. These microorganisms frequently exchange materials with the host. Melatonin isomers, which are produced by these organisms inevitably enter the host's system. The origins of melatonin and its isomers can be traced back to photosynthetic bacteria and other primitive unicellular organisms. Since some of these bacteria are believed to be the precursors of mitochondria and chloroplasts these cellular organelles may be the primary sites of melatonin production in animals or in plants, respectively. Phylogenic analysis based on its rate-limiting synthetic enzyme, serotonin N-acetyltransferase (SNAT), indicates its multiple origins during evolution. Therefore, it is likely that melatonin and its isomer are also present in the domain of archaea, which perhaps require these molecules to protect them against hostile environments including extremely high or low temperature. Evidence indicates that the initial and primary function of melatonin and its isomers was to serve as the first-line of defence against oxidative stress and all other functions were acquired during evolution either by the process of adoption or by the extension of its antioxidative capacity.
authors.affiliation: Department of Cellular and Structural Biology, the University of Texas, Health Science Center, San Antonio, TX 78229, USA. tan@uthscsa.edu.
authors.forename: Dun-Xian
authors.initials: DX
authors.lastname: Tan
authors.affiliation: Institute for Horticultural Plants, China Agricultural University, Beijing 100083, China. zheng.xiao.d@163.com.
authors.forename: Xiaodong
authors.initials: X
authors.lastname: Zheng
authors.affiliation: Institute for Horticultural Plants, China Agricultural University, Beijing 100083, China. 05021@cau.edu.cn.
authors.forename: Jin
authors.initials: J
authors.lastname: Kong
authors.affiliation: Department of Cellular and Structural Biology, the University of Texas, Health Science Center, San Antonio, TX 78229, USA. lmanchester@stmarytx.edu.
authors.forename: Lucien C
authors.initials: LC
authors.lastname: Manchester
authors.affiliation: Johann Friedrich Blumenbach Institute of Zoology and Anthropology, University of Göttingen, Göttingen 37073, Germany. rhardel@gwdg.de.
authors.forename: Ruediger
authors.initials: R
authors.lastname: Hardeland
authors.affiliation: Department of Cellular and Structural Biology, the University of Texas, Health Science Center, San Antonio, TX 78229, USA. skim@dongduk.ac.kr.
authors.forename: Seok Joong
authors.initials: SJ
authors.lastname: Kim
authors.affiliation: Department of Cellular and Structural Biology, the University of Texas, Health Science Center, San Antonio, TX 78229, USA. xxy2006stone@163.com.
authors.forename: Xiaoying
authors.initials: X
authors.lastname: Xu
authors.affiliation: Department of Cellular and Structural Biology, the University of Texas, Health Science Center, San Antonio, TX 78229, USA. reiter@uthscsa.edu.
authors.forename: Russel J
authors.initials: RJ
authors.lastname: Reiter
mesh_terms: D000818:Animals; D001105:Archaea / Q000145:classification / Q000378:metabolism; D047068:Arylalkylamine N-Acetyltransferase / Q000737:chemistry / Q000378:metabolism; D005075:Biological Evolution; D007536:Isomerism; D008550:Melatonin / Q000737:chemistry / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism; D010944:Plants / Q000145:classification / Q000378:metabolism
chemical_list: D047068:Arylalkylamine N-Acetyltransferase; D008550:Melatonin