title: Enzymatic features of serotonin biosynthetic enzymes and serotonin biosynthesis in plants.
abstract: Serotonin, a pineal hormone in mammals, is found in a wide range of plant species at detection levels from a few nanograms to a few milligrams, and has been implicated in several physiological roles, such as flowering, morphogenesis and adaptation to environmental changes. Serotonin synthesis requires two enzymes, tryptophan decarboxylase (TDC) and tryptamine 5-hydroxylase (T5H), with TDC serving as a rate-limiting step because of its high K(m) relation to the substrate tryptophan (690 microM) and its undetectable expression level in control plants. However, T5H and downstream enzymes, such as serotonin N-hydroxycinnamoyl transferase (SHT), have low K(m) values with corresponding substrates. This suggests that the biosynthesis of serotonin or serotonin-derived secondary metabolites is restricted to cellular stages when high tryptophan levels are present.
authors.affiliation: Department of Molecular Biotechnology; Agricultural Plant Stress Research Center; Biotechnology Research Institute; Chonnam National University; Gwangju, Korea.
authors.forename: Kiyoon
authors.initials: K
authors.lastname: Kang
authors.forename: Sei
authors.initials: S
authors.lastname: Kang
authors.forename: Kyungjin
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authors.lastname: Lee
authors.forename: Munyoung
authors.initials: M
authors.lastname: Park
authors.forename: Kyoungwhan
authors.initials: K
authors.lastname: Back
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