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Skeletal formula of the L-isomer
Skeletal formula of L-tyrosine

L-Tyrosine at physiological pH
IUPAC name
Other names
L-2-Amino-3-(4-hydroxyphenyl)propanoic acid
3D model (
ECHA InfoCard
100.000.419 Edit this at Wikidata
  • InChI=1S/C9H11NO3/c10-8(9(12)13)5-6-1-3-7(11)4-2-6/h1-4,8,11H,5,10H2,(H,12,13)/t8-/m0/s1 checkY
  • N[C@@H](Cc1ccc(O)cc1)C(O)=O
  • Zwitterion: [NH3+][C@@H](Cc1ccc(O)cc1)C([O-])=O
Molar mass 181.191 g·mol−1
Appearance white solid
.0453 g/100 mL
-105.3·10−6 cm3/mol
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineFlammability 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g. canola oilInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
Supplementary data page
Tyrosine (data page)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

L-Tyrosine or tyrosine (symbol Tyr or Y)

non-essential amino acid with a polar side group. The word "tyrosine" is from the Greek tyrós, meaning cheese, as it was first discovered in 1846 by German chemist Justus von Liebig in the protein casein from cheese.[3][4] It is called tyrosyl when referred to as a functional group or side chain. While tyrosine is generally classified as a hydrophobic amino acid, it is more hydrophilic than phenylalanine.[5] It is encoded by the codons UAC and UAU in messenger RNA

The one-letter symbol Y was assigned to tyrosine for being alphabetically nearest of those letters available. Note that T was assigned to the structurally simpler threonine, U was avoided for its similarity with V for valine, W was assigned to tryptophan, while X was reserved for undetermined or atypical amino acids.[6] The mnemonic tYrosine was also proposed.[7]


Aside from being a

ester linkage, with phosphate in particular. Phosphate groups are transferred to tyrosine residues by way of protein kinases. This is one of the post-translational modifications. Phosphorylated tyrosine occurs in proteins that are part of signal transduction

Similar functionality is also presented in serine and threonine, whose side chains have a hydroxy group, but are alcohols. Phosphorylation of these three amino acids' moieties (including tyrosine) creates a negative charge on their ends, that is greater than the negative charge of the only negatively charged aspartic and glutamic acids. Phosphorylated proteins keep these same properties—which are useful for more reliable protein-protein interactions—by means of phosphotyrosine, phosphoserine and phosphothreonine.[8]

Binding sites for a signalling phosphoprotein may be diverse in their chemical structure.[9]

Phosphorylation of the hydroxyl group can change the activity of the target protein, or may form part of a signaling cascade via SH2 domain binding.[10]

A tyrosine residue also plays an important role in photosynthesis. In chloroplasts (photosystem II), it acts as an electron donor in the reduction of oxidized chlorophyll. In this process, it loses the hydrogen atom of its phenolic OH-group. This radical is subsequently reduced in the photosystem II by the four core manganese clusters.[11]

Dietary requirements and sources

The Dietary Reference Intake for tyrosine is usually estimated together with phenylalanine. It varies depending on an estimate method, however the ideal proportion of these two amino acids is considered to be 60:40 (phenylalanine:tyrosine) as a human body has such composition.[12] Tyrosine, which can also be synthesized in the body from phenylalanine, is found in many high-

soy protein and lima beans.[13][14] For example, the white of an egg has about 250 mg per egg,[15] while beef, lamb, pork, tuna, salmon, chicken, and turkey contain about 500–1000 mg per 3 ounces (85 g) portion.[15][16]



In plants and most microorganisms, tyrosine is produced via


Mammals synthesize tyrosine from the essential amino acid phenylalanine (Phe), which is derived from food. The conversion of Phe to Tyr is catalyzed by the enzyme phenylalanine hydroxylase, a monooxygenase. This enzyme catalyzes the reaction causing the addition of a hydroxyl group to the end of the 6-carbon aromatic ring of phenylalanine, such that it becomes tyrosine.


Conversion of phenylalanine and tyrosine to its biologically important derivatives.

Phosphorylation and sulfation

Some of the tyrosine residues can be tagged (at the hydroxyl group) with a phosphate group (phosphorylated) by protein kinases. In its phosphorylated form, tyrosine is called phosphotyrosine. Tyrosine phosphorylation is considered to be one of the key steps in signal transduction and regulation of enzymatic activity. Phosphotyrosine can be detected through specific antibodies. Tyrosine residues may also be modified by the addition of a sulfate group, a process known as tyrosine sulfation.[17] Tyrosine sulfation is catalyzed by tyrosylprotein sulfotransferase (TPST). Like the phosphotyrosine antibodies mentioned above, antibodies have recently been described that specifically detect sulfotyrosine.[18]

Precursor to neurotransmitters and hormones

In dopaminergic cells in the



thyroxine (T4) in the colloid of the thyroid
are also derived from tyrosine.

Biosynthetic pathways for catecholamines and trace amines in the human brain[19][20][21]
The image above contains clickable links
Tyrosine is a precursor to trace amine compounds and the catecholamines.

Precursor to other compounds

The latex of

p-coumaric acid.Tyrosine is also the precursor to the pigment melanin. Tyrosine (or its precursor phenylalanine) is needed to synthesize the benzoquinone structure which forms part of coenzyme Q10.[23][24]


fumarate. Two dioxygenases are necessary for the decomposition path. The end products can then enter into the citric acid cycle.

[citation needed


The decomposition of L-tyrosine (syn. para-hydroxyphenylalanine) begins with an α-ketoglutarate dependent

. The positional description para, abbreviated p, mean that the hydroxyl group and side chain on the phenyl ring are across from each other (see the illustration below).

The next oxidation step catalyzes by

is created.

coenzyme. Fumarylacetoacetate is finally split by the enzyme fumarylacetoacetate hydrolase
through the addition of a water molecule.


ketone body, which is activated with succinyl-CoA, and thereafter it can be converted into acetyl-CoA, which in turn can be oxidized by the citric acid cycle or be used for fatty acid synthesis

Phloretic acid is also a urinary metabolite of tyrosine in rats.[26]

Ortho- and meta-tyrosine

free radicals
(middle and bottom).


free-radical hydroxylation of phenylalanine under conditions of oxidative stress.[27][28]

Medical use

Tyrosine is a precursor to neurotransmitters and increases plasma neurotransmitter levels (particularly dopamine and norepinephrine),[29] but has little if any effect on mood in normal subjects.[30][31][32]

A 2015 systematic review found that "tyrosine loading acutely counteracts decrements in working memory and information processing that are induced by demanding situational conditions such as extreme weather or cognitive load" and therefore "tyrosine may benefit healthy individuals exposed to demanding situational conditions".[33]

Industrial synthesis

L-tyrosine is used in

food additives. Two methods were formerly used to manufacture L-tyrosine. The first involves the extraction of the desired amino acid from protein hydrolysates using a chemical approach. The second utilizes enzymatic synthesis from phenolics, pyruvate, and ammonia through the use of tyrosine phenol-lyase.[34] Advances in genetic engineering and the advent of industrial fermentation have shifted the synthesis of L-tyrosine to the use of engineered strains of E. coli.[35][34]

See also


  1. ^ .
  2. ^ "Nomenclature and Symbolism for Amino Acids and Peptides". IUPAC-IUB Joint Commission on Biochemical Nomenclature. 1983. Archived from the original on 9 October 2008. Retrieved 5 March 2018.
  3. ^ "Tyrosine". The Columbia Electronic Encyclopedia, 6th ed. Infoplease.com — Columbia University Press. 2007. Retrieved 2008-04-20.
  4. ^ Harper D (2001). "Tyrosine". Online Etymology Dictionary. Retrieved 2008-04-20.
  5. ^ "Amino Acids - Tyrosine". www.biology.arizona.edu. Retrieved 2018-01-31.
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  13. ^ Nutient Ranking Tool. MyFoodData.com. https://tools.myfooddata.com/nutrient-ranking-tool/tyrosine/all/highest
  14. ^ "Tyrosine". University of Maryland Medical Center. Archived from the original on 2013-06-04. Retrieved 2011-03-17.
  15. ^ a b Top 10 Foods Highest in Tyrosine
  16. ^ Nutient Ranking Tool. MyFoodData.com. https://tools.myfooddata.com https://tools.myfooddata.com/nutrient-ranking-tool/tyrosine/meats/highest/ounces/common/no
  17. PMID 17046811
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External links