Toxicity of meta-Tyrosine.

Marcin Tyminski,Urszula Krasuska,Agnieszka Gniazdowska,Katarzyna Ciacka,Pawel Staszek

doi:10.3390/plants10122800

Marcin Tyminski, Urszula Krasuska + Show 3 more

Open Access

https://doi.org/10.3390/plants10122800

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Abstract

L-Tyrosine (Tyr) is one of the twenty proteinogenic amino acids and also acts as a precursor for secondary metabolites. Tyr is prone to modifications, especially under conditions of cellular redox imbalance. The oxidation of Tyr precursor phenylalanine leads to the formation of Tyr non-proteinogenic isomers, including meta-Tyr (m-Tyr), a marker of oxidative stress. The aim of this review is to summarize the current knowledge on m-Tyr toxicity. The direct m-Tyr mode of action is linked to its incorporation into proteins, resulting in their improper conformation. Furthermore, m-Tyr produced by some plants as an allelochemical impacts the growth and development of neighboring organisms. In plants, the direct harmful effect of m-Tyr is due to its modification of the proteins structure, whereas its indirect action is linked to the disruption of reactive oxygen and nitrogen species metabolism. In humans, the elevated concentration of m-Tyr is characteristic of various diseases and ageing. Indeed, m-Tyr is believed to play an important role in cancer physiology. Thus, since, in animal cells, m-Tyr is formed directly in response to oxidative stress, whereas, in plants, m-Tyr is also synthesized enzymatically and serves as a chemical weapon in plant–plant competition, the general concept of m-Tyr role in living organisms should be specified.

Highlights

Twenty canonical amino acids (AAs) are the base of the proteins structure in living organisms
Some of the non-proteinogenic amino acids (NPAAs) are described as antimetabolites, analogs of proteinogenic AAs, and serve as toxins
The negative effect of a specific NPAA may be removed by the application of its proteinogenic analog

Summary

Introduction

Twenty canonical amino acids (AAs) are the base of the proteins structure in living organisms. Chorismate, the final product of the shikimate pathway, is a precursor for Phe and Tyr biosynthesis in plants, bacteria, and fungi ([16] and references ). AAcccocrodrdininggtoto[4[]4]wwitihthsosommeemmooddifiificacatitoionns.s. Depending on the location of a hydroxyl group in the benzyl ring, three structural Tyr isomers are described: (i) para-(p-Tyr), which is the most common product of metabolic reactions integrated into proteins; and (ii) meta-(m-Tyr) and (iii) ortho-(o-Tyr), which are both products of the oxidation of Phe, known as markers of oxidative stress [18]. Tyr non-proteinogenic isomers can emerge during the exposure of Phe to highly energetic radiation or in the reaction with peroxynitrite (ONOO−), a compound formed from the superoxide anion (O2−) and nitric oxide (NO). The hydroxylation of Phe in the presence of ONOO− occurs partially via hydroxyl radicals formation [23]

Fescue as the Biological Source of m-Tyr

Mode of Action of m-Tyr

Findings

Summary