Archives

  • 2018-07
  • 2019-04
  • 2019-05
  • 2019-06
  • 2019-07
  • 2019-08
  • 2019-09
  • 2019-10
  • 2019-11
  • 2019-12
  • 2020-01
  • 2020-02
  • 2020-03
  • 2020-04
  • 2020-05
  • 2020-06
  • 2020-07
  • 2020-08
  • 2020-09
  • 2020-10
  • 2020-11
  • 2020-12
  • 2021-01
  • 2021-02
  • 2021-03
  • 2021-04
  • 2021-05
  • 2021-06
  • 2021-07
  • 2021-08
  • 2021-09
  • 2021-10
  • 2021-11
  • 2021-12
  • 2022-01
  • 2022-02
  • 2022-03
  • 2022-04
  • 2022-05
  • 2022-06
  • 2022-07
  • 2022-08
  • 2022-09
  • 2022-10
  • 2022-11
  • 2022-12
  • 2023-01
  • 2023-02
  • 2023-03
  • 2023-04
  • 2023-05
  • 2023-06
  • 2023-07
  • 2023-08
  • 2023-09
  • 2023-10
  • 2023-11
  • 2023-12
  • 2024-01
  • 2024-02
  • 2024-03
  • 2024-04

    • The mode of action of m Tyr has

    2021-09-22

    The mode of action of m-Tyr has not been fully recognized. The primary/basic mechanism of action of m-Tyr is thought to be associated with the incorporation of this NPAA into the structure of proteins resulting in formation of dysfunctional proteins [11], [12]. m-Tyr is incorporated into proteins in vitro by a mechanism involving l-phenylalanine-tRNA synthetase [13]. Another hypothesis points that m-Tyr could be converted into dihydroxyphenylalanine (l-DOPA) and as such acts as potential phytotoxic agent [14]. Recently, a large body of literature has been published describing the changes in metabolism of reactive oxygen species (ROS) of the acceptor plant as potential mechanism of action of various phytotoxic substances, including allelochemicals (see Ref. [15] for review). Oxidative stress due to the excessive production of ROS and the lower efficiency of antioxidant system may be the first measurable effect of action of allelotoxins including m-Tyr. Further evidence has shown correlation between increase in the concentration of m-Tyr and excessive ROS production in the tissues of living organisms, especially animals, including humans [16]. In animal cells m-Tyr is considered as a marker of oxidative stress [17], [18], [19]. Accumulation of m-Tyr is related to such diseases as: Alzheimer's, atherosclerosis or diabetes [16], [20]. Progression of neurodegenerative or cardiovascular illnesses is linked not only to ROS overproduction but also to disturbances in nitric oxide (NO) and other reactive nitrogen species (RNS) biosynthesis and metabolism [21], [22]. Both in animal and plant organisms NO is recognized as a signaling molecule, action of which (despite other pathways) depends on modification of the structure of proteins [23], [24], [25]. Most of these modifications result from the actions of NO with ROS to produce reactive oxidants. The oxidants modify the proteins by S-nitrosylation of thiol groups or nitration of aromatic Conoidin A e.g. Tyr, by formation of 3-nitro Tyr (3-NT). Tyr nitration is the reaction of a nitrating agent with a Tyr residue of a target protein that lead to the addition of a nitro group (NO2) in the ortho position of the phenolic hydroxyl group. The NO2 group originates mainly from peroxynitrite (ONOO−), which is generated in reaction of superoxide anion (O2-) and NO [24], [26]. Cellular concentration of NO depends on its biosynthesis and scavenging [26], [27]. Glutathione (GSH), despite its action as an antioxidant, reacts also with NO leading to formation of nitrosoglutathione (GSNO). This molecule is a major cellular bio-reservoir of NO. The GSNO pool is regulated by activity of GSNO reductase (GSNOR), formerly known as glutathione-dependent formaldehyde dehydrogenase (FALDH; EC 1.2.1.1), which converts GSNO into oxidized form of glutathione (GSSG) and ammonia [28]. According to formal enzyme classification, GSNOR belongs to a family of Zn-dependent class III alcohol dehydrogenases (ADH3; EC 1.1.1.1). GSNOR has important role in the regulation of GSNO content in plants during development and under stress conditions (see Ref. [28] for review). Xu et al. [29] suggested even that GSNOR facilitates multiple homeostatic and stress adaptation processes in plants. At present, there is no data evaluating disturbances in ROS and RNS level/metabolism as the mechanism of phytotoxicity of m-Tyr in plant tissues. Recently we have shown that l-canavanine's (another toxic NPAA) mode of action is associated with accumulation of ROS and alterations in RNS level coupled to enhanced protein carbonylation [30], [31]. Taking to account that m-Tyr is considered as an indicator of oxidative stress, we suspect that its supplementation may impact also RNS metabolism and content, and in consequence influence protein nitration, one of RNS-regulated protein posttranslational modifications (PTMs). Protein nitration is as a reliable marker of nitrosative stress and seems to be typical for plants responding to various unfavorable conditions of both biotic (pathogens) or abiotic nature (see Refs. [32], [33] for review).