Aromatic amino acids

Phenylalanine

Tryptophan

Tyrosine

Thyroxine

Aromatic amino acids (AAA)^[1] are amino acids that include an aromatic ring.

Examples include:

• Among 20 standard amino acids:
  • Phenylalanine
  • Tryptophan
  • Tyrosine
  • Histidine
• Others:
  • Thyroxine
  • 5-Hydroxytryptophan
  • L-DOPA

Phenylalanine → Tyrosine → L-DOPA → (Dopamine) → (Epinephrine) → (Norepinephrine)

Tryptophan → 5-hydroxytryptophan → (Serotonin)

Phenylalanine → Tyrosine → Thyroxine

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.

Aromatic amino acids are able to absorb light due to their conjugated double bonds. This characteristic of aromatic amino acids is used to quantify the concentration of proteins in an unknown sample. These amino acids are able to absorb light which excites its electron to the excited state. When the electron falls back to its ground state, it will either emit light or release energy. If the molecule is able to emit light it is known as a fluorescent molecule. Tryptophan is widely used as a fluorescent molecule.^[2]

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.^[3]

See also

• Aromatic L-amino acid decarboxylase

References

External links

• Aromatic Amino Acids at the US National Library of Medicine Medical Subject Headings (MeSH)

Further reading

• Maeda, H.; Dudareva, N. (2012). "The Shikimate Pathway and Aromatic Amino Acid Biosynthesis in Plants". Annual Review of Plant Biology. 63: 73–105. PMID 22554242. doi:10.1146/annurev-arplant-042811-105439. 

Metabolism map

Carbon Fixation Photo- respiration Pentose Phosphate Pathway Citric Acid Cycle Glyoxylate Cycle Urea Cycle Fatty Acid Synthesis Fatty Acid Elongation Beta Oxidation Peroxisomal Beta Oxidation Glyco- genolysis Glyco- genesis Glyco- lysis Gluconeo- genesis Decarb- oxylation Fermentation Keto- lysis Keto- genesis feeders to Gluconeo- genesis Direct / C4 / CAM Carbon Intake Light Reaction Oxidative Phosphorylation Amino Acid Deamination Citrate Shuttle Lipogenesis Lipolysis Steroidogenesis MVA Pathway MEP Pathway Shikimate Pathway Transcription & Replication Translation Proteolysis Glycosy- lation Sugar Acids Double/Multiple Sugars & Glycans Simple Sugars Inositol-P Amino Sugars & Sialic Acids Nucleotide Sugars Hexose-P Triose-P Glycerol P-glycerates Pentose-P Tetrose-P Propionyl -CoA Succinate Acetyl -CoA Pentose-P P-glycerates Glyoxylate Photosystems Pyruvate Lactate Acetyl -CoA Citrate Oxalo- acetate Malate Succinyl -CoA α-Keto- glutarate Ketone Bodies Respiratory Chain Serine Group Alanine Branched-chain Amino Acids Aspartate Group Homoserine Group & Lysine Glutamate Group & Proline Arginine Creatine & Polyamines Ketogenic & Glucogenic Amino Acids Amino Acids Shikimate Aromatic Amino Acids & Histidine Ascorbate (Vitamin C) δ-ALA Bile Pigments Hemes Cobalamins (Vitamin B12) Various Vitamin B's Calciferols (Vitamin D) Retinoids (Vitamin A) Quinones (Vitamin K) & Carotenoids (Vitamin E) Cofactors Vitamins & Minerals Antioxidants PRPP Nucleotides Nucleic Acids Proteins Glycoproteins & Proteoglycans Chlorophylls MEP MVA Acetyl -CoA Polyketides Terpenoid Backbones Terpenoids & Carotenoids (Vitamin A) Cholesterol Bile Acids Glycero- phospholipids Glycerolipids Acyl-CoA Fatty Acids Glyco- sphingolipids Sphingolipids Waxes Polyunsaturated Fatty Acids Neurotransmitters & Thyroid Hormones Steroids Endo- cannabinoids Eicosanoids Major metabolic pathways in metro-style map. Click any text (name of pathway or metabolites) to link to the corresponding article. Single lines: pathways common to most lifeforms. Double lines: pathways not in humans (occurs in e.g. plants, fungi, prokaryotes). Orange nodes: carbohydrate metabolism. Violet nodes: photosynthesis. Red nodes: cellular respiration. Pink nodes: cell signaling. Blue nodes: amino acid metabolism. Grey nodes: vitamin and cofactor metabolism. Brown nodes: nucleotide and protein metabolism. Green nodes: lipid metabolism.