China
Africa
Explore chapters and articles related to this topic
Roles of Melatonin in Maintaining Mitochondrial Welfare
Published in Shamim I. Ahmad, Handbook of Mitochondrial Dysfunction, 2019
Feres José Mocayar Marón, Emiliano Diez, Russel J. Reiter, Walter Manucha
Melatonin synthesis and secretion were initially described in the pineal gland; its synthesis is regulated by the environmental light/dark cycle via the suprachiasmatic nucleus. The pineal gland is part of the photoneuroendocrine system, and acts as a transducer, converting afferent neurally-coded photic information into melatonin, the chemical expression of darkness5. The precursors of melatonin are the aromatic amino acid tryptophan and serotonin. The pineal parenchyma captures tryptophan; then it is hydroxylated and decarboxylated to serotonin. Serotonin is then N-acetylated by the enzyme aralkylamine N-acetyltransferase (AANAT), and finally, the product is converted into melatonin by the N-Acetylserotonin-O-methyltransferase (ASMT), also known as hydroxyindole-O-methyltransferase (HIOMT)6. Melatonin is not stored within the gland but quickly diffuses into the bloodstream and cerebrospinal fluid7.
The Multi-Regulatory Properties of Melatonin in Plants
Published in Akula Ramakrishna, Victoria V. Roshchina, Neurotransmitters in Plants, 2018
Marino B. Arnao, Josefa Hernández-Ruiz
Chemically, melatonin (N-acetyl-5-methoxytryptamine) is an indolic compound derived from serotonin (5-hydroxytryptamine) (Figure 5.1). Both biogenic amines are synthesized from the amino acid tryptophan in an extensively studied biosynthetic pathway in both animals and plants (Reiter, 1991; Arnao and Hernández-Ruiz, 2006, 2014a, 2015a, 2015b; Tan et al., 2015; Back et al., 2016; Nawaz et al., 2016). In plants, tryptophan is converted into tryptamine by tryptophan decarboxylase (TDC) (Figure 5.1). Tryptamine is then converted into 5-hydroxytryptamine (commonly known as serotonin) by tryptamine 5-hydroxylase (T5H), an enzyme that has been only characterized in rice, and which possibly acts with a large number of substrates, although this has not been studied in depth (Kang et al., 2007; Fujiwara et al., 2010; Park et al., 2012, 2013b). The N-acetylation of serotonin is catalyzed by the enzyme serotonin N-acetyltransferase (SNAT) (Ferry et al., 2000; Byeon et al., 2015b, 2016). N-acetylserotonin is then methylated by acetylserotonin-O-methyltransferase (ASMT), a hydroxyindole-O-methyltransferase that generates melatonin. In plants, the methylation of N-acetylserotonin can also be made by a caffeic acid O-methyltransferase (COMT), an enzyme that can act on a broad diversity of substrates including caffeic acid and quercetin (Byeon et al., 2014a, 2015a; Lee et al., 2014b). Serotonin can also be transformed into 5-methoxytryptamine by ASMT (and by COMT), and then generate melatonin through the action of SNAT. Also, melatonin can be generated through the formation of N-acetyltryptamine, which is converted into N-acetylserotonin. Finally, serotonin can be formed from 5-hydroxytryptophan, after the action of tryptophan hydroxylase (TPH) and TDC, the latter step occurring mainly in animals but also in plants to a lesser extent.
Diurnal and circadian variations in indole contents in the goose pineal gland
Published in Chronobiology International, 2018
N. Ziółkowska, B. Lewczuk, M. Prusik
AA-NAT and ASMT are considered to be the most important enzymes with respect to the final levels of pineal indoles, and to affect the diurnal variation of these compounds. Studies conducted with rodents and birds strongly suggest that, whereas AA-NAT is responsible for diurnal changes in melatonin synthesis, ASMT is the rate-limiting enzyme for night-time melatonin production (Adamska et al. 2016a; Chattoraj et al. 2009; Liu and Borjigin 2005; Lewczuk et al. 2014). Also, a recent study has suggested that AADC may play an important role in the regulation of serotonin levels, and indirectly, melatonin levels, in the pineal gland of young chickens (Adamska et al. 2016a).