Aromatic amino acid
- Among 20 standard amino acids:
Phenylalanine, tryptophan, and histidine are essential amino acids for animals. Since they are not synthesized in the human body, they must be derived from the diet. Tyrosine is semi-essential; it can be synthesized, but only from phenylalanine. A lack of the enzyme phenylalanine hydroxylase, used in tyrosine synthesis, causes phenylketonuria and concurrently renders tyrosine an essential amino acid.
Amino acids do not absorb light in the visible region, however aromatic amino acids absorb ultraviolet radiation above 250 nm. This characteristic of aromatic amino acids is used in quantitative analysis.
Animals obtain aromatic amino acids from their diet, but all plants and micro-organisms must synthesize their aromatic amino acids through the metabolically costly shikimate pathway in order to make them.
In plants, the shikimate pathway first leads to the formation of chorismate, which is the precursor of phenylalanine, tyrosine, and tryptophan. These aromatic amino acids are the derivatives of many secondary metabolites, all essential to a plant's biological functions, such as the hormones salicylate and auxin. This pathway contains enzymes that can be regulated by inhibitors, which can cease the production of chorismate, and ultimately the organism's biological functions. Herbicides and antibiotics work by inhibiting these enzymes involved in the biosynthesis of aromatic amino acids, thereby rendering them toxic to plants. Glyphosate, a type of herbicide, is used to control the accumulation of excess greens. In addition to destroying greens, Glyphosate can easily affect the maintenance of the gut microbiota in host organisms by specifically inhibiting the 5-enolpyruvylshikinate-3-phosphate synthase which prevents the biosynthesis of essential aromatic amino acids. Inhibition of this enzyme results in disorders such as gastrointestinal diseases and metabolic diseases. 
- Logan, Carolynn M.; Rice, M. Katherine (1987). Logan's Medical and Scientific Abbreviations. Philadelphia: J. B. Lippincott Company. p. 3. ISBN 978-0-397-54589-6.
- Möller, Matías; Denicola, Ana (2002-05-01). "Protein tryptophan accessibility studied by fluorescence quenching". Biochemistry and Molecular Biology Education. 30 (3): 175–178. doi:10.1002/bmb.2002.494030030035. ISSN 1539-3429.
- Tzin, Vered; Galili, Gad (2010-05-17). "The Biosynthetic Pathways for Shikimate and Aromatic Amino Acids in Arabidopsis thaliana". The Arabidopsis Book / American Society of Plant Biologists. 8: e0132. doi:10.1199/tab.0132. ISSN 1543-8120. PMC 3244902. PMID 22303258.
- "Glyphosate has limited short-term effects on commensal bacterial community composition in the gut environment due to sufficient aromatic amino acid levels". Environmental Pollution. 233: 364–376. February 2018. doi:10.1016/j.envpol.2017.10.016.