From HandWiki
Short description: Amino acid
Skeletal formula of the L-isomer
Skeletal formula of L-tyrosine
L-Tyrosin phys.svg
L-Tyrosine at physiological pH
IUPAC name
Other names
L-2-Amino-3-(4-hydroxyphenyl)propanoic acid
3D model (JSmol)
Molar mass 181.191 g·mol−1
.0453 g/100 mL
-105.3·10−6 cm3/mol
NFPA 704 (fire diamond)
Flammability code 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g. canola oilHealth code 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no codeNFPA 704 four-colored diamond
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

L-Tyrosine or tyrosine (symbol Tyr or Y)[2] or 4-hydroxyphenylalanine is one of the 20 standard amino acids that are used by cells to synthesize proteins. It is a 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.


Aside from being a proteinogenic amino acid, tyrosine has a special role by virtue of the phenol functionality. It occurs in proteins that are part of signal transduction processes and functions as a receiver of phosphate groups that are transferred by way of protein kinases. 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.

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.

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.[6] Tyrosine, which can also be synthesized in the body from phenylalanine, is found in many high-protein food products such as chicken, turkey, fish, milk, yogurt, cottage cheese, cheese, peanuts, almonds, pumpkin seeds, sesame seeds, soy products and lima beans, but also in avocados and bananas.[7] For example, the white of an egg has about 250 mg per egg,[8] while lean beef, lamb, pork, salmon, chicken, and turkey contain about 1 g per 3 ounces (85 g) portion.[8]


Plant biosynthesis of tyrosine from prephenate.

In plants and most microorganisms, tyrosine is produced via prephenate, an intermediate on the shikimate pathway. Prephenate is oxidatively decarboxylated with retention of the hydroxyl group to give p-hydroxyphenylpyruvate, which is transaminated using glutamate as the nitrogen source to give tyrosine and α-ketoglutarate.

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.[9] Tyrosine sulfation is catalyzed by tyrosylprotein sulfotransferase (TPST). Like the phosphotyrosine antibodies mentioned above, antibodies have recently been described that specifically detect sulfotyrosine.[10]

Precursor to neurotransmitters and hormones

In dopaminergic cells in the brain, tyrosine is converted to L-DOPA by the enzyme tyrosine hydroxylase (TH). TH is the rate-limiting enzyme involved in the synthesis of the neurotransmitter dopamine. Dopamine can then be converted into other catecholamines, such as norepinephrine (noradrenaline) and epinephrine (adrenaline).

The thyroid hormones triiodothyronine (T3) and thyroxine (T4) in the colloid of the thyroid are also derived from tyrosine. {{Annotated image 4 | caption = {{{caption|In humans, catecholamines and phenethylaminergic trace amines are derived from the amino acid {{nowrap|L-phenylalanine}}.}}} | header_background = #F0F8FF | header = Biosynthetic pathways for catecholamines and trace amines in the human brain<ref name="Trace amine template 1">Broadley KJ (March 2010). "The vascular effects of trace amines and amphetamines". Pharmacol. Ther. 125 (3): 363–375. doi:10.1016/j.pharmthera.2009.11.005. PMID 19948186. </ref>[11][12] | alt = Graphic of catecholamine and trace amine biosynthesis | image = Catecholamine and trace amine biosynthesis.png | image-width = 580 | image-left = 5 | image-top = 0 | align = center | width = 590 | height = 585 | annot-font-size = 14 | annot-text-align = center | annotations =


{{annotation|50|565|{{if pagename|Adrenaline=Adrenaline|Epinephrine=Epinephrine|Catecholamine=Epinephrine|other=Epinephrine}}}}

{{annotation|245|60|{{if pagename|Phenethylamine=Phenethylamine|Trace amine=Phenethylamine|Neurobiological effects of physical exercise={{highlight|Phenethylamine}}|other=Phenethylamine}}}}

{{annotation|245|565|{{if pagename|Norepinephrine=Norepinephrine|Adrenaline=Noradrenaline|Catecholamine=Norepinephrine|other=Norepinephrine}}}}



Precursor to alkaloids

The latex of Papaver somniferum, the opium poppy, has been shown to convert tyrosine into the alkaloid morphine and the bio-synthetic pathway has been established from tyrosine to morphine by using Carbon-14 radio-labelled tyrosine to trace the in-vivo synthetic route.[13]

Precursor to natural phenols

Tyrosine ammonia lyase (TAL) is an enzyme in the natural phenols biosynthesis pathway. It transforms L-tyrosine into p-coumaric acid.

Precursor to pigments

Tyrosine is also the precursor to the pigment melanin.

Role in coenzyme Q10 synthesis

Tyrosine (or its precursor phenylalanine) is needed to synthesize the benzoquinone structure which forms part of coenzyme Q10.


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

The decomposition of L-tyrosine (syn. para-hydroxyphenylalanine) begins with an α-ketoglutarate dependent transamination through the tyrosine transaminase to para-hydroxyphenylpyruvate. 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 p-hydroxyphenylpyruvate dioxygenase and splitting off CO2 homogentisate (2,5-dihydroxyphenyl-1-acetate).[14] In order to split the aromatic ring of homogentisate, a further dioxygenase, homogentisate 1,2-dioxygenase is required. Thereby, through the incorporation of a further O2 molecule, maleylacetoacetate is created.

Fumarylacetoacetate is created by maleylacetoacetate cis-trans-isomerase through rotation of the carboxyl group created from the hydroxyl group via oxidation. This cis-trans-isomerase contains glutathione as a coenzyme. Fumarylacetoacetate is finally split by the enzyme fumarylacetoacetate hydrolase through the addition of a water molecule.

Thereby fumarate (also a metabolite of the citric acid cycle) and acetoacetate (3-ketobutyroate) are liberated. Acetoacetate is a 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.[15]

Ortho- and meta-tyrosine

Enzymatic oxidation of tyrosine by phenylalanine hydroxylase (top) and non-enyzmatic oxidation by hydroxyl free radicals (middle and bottom).

Three structural isomers of L-tyrosine are known. In addition to the common amino acid L-tyrosine, which is the para isomer (para-tyr, p-tyr or 4-hydroxyphenylalanine), there are two additional regioisomers, namely meta-tyrosine (also known as 3-hydroxyphenylalanine, L-m-tyrosine, and m-tyr) and ortho-tyrosine (o-tyr or 2-hydroxyphenylalanine), that occur in nature. The m-tyr and o-tyr isomers, which are rare, arise through non-enzymatic free-radical hydroxylation of phenylalanine under conditions of oxidative stress.[16][17]

m-Tyrosine and analogues (rare in nature but available synthetically) have shown application in Parkinson's disease, Alzheimer's disease and arthritis.[18]

Medical use

Tyrosine is a precursor to neurotransmitters and increases plasma neurotransmitter levels (particularly dopamine and norepinephrine),[19] but has little if any effect on mood in normal subjects.[20][21][22] A number of studies have found tyrosine is useful during stress, cold, fatigue (in mice),[23][24] prolonged work and sleep deprivation,[25][26] with reductions in stress hormone levels,[27] reductions in stress-induced weight loss seen in animal trials,[24] and improvements in cognitive and physical performance[21][28][29] seen in human trials.

Tyrosine does not seem to have any significant effect on cognitive or physical performance in normal circumstances,[30][31] but does help sustain working memory better during multitasking.[32]


It is unknown if MAOIs interact with tyrosine.[33]

Industrial synthesis

L-tyrosine and its derivatives (L-DOPA, melanin, phenylpropanoids, and others) are used in pharmaceuticals, dietary supplements, and 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. 1.0 1.1 "Precision neutron diffraction structure determination of protein and nucleic acid components. X. A comparison between the crystal and molecular structures of L‐tyrosine and L‐tyrosine hydrochloride". J. Chem. Phys. 58 (6): 2547–2556. 1973. doi:10.1063/1.1679537. Bibcode1973JChPh..58.2547F. 
  2. "Nomenclature and Symbolism for Amino Acids and Peptides". IUPAC-IUB Joint Commission on Biochemical Nomenclature. 1983. 
  3. "Tyrosine". The Columbia Electronic Encyclopedia, 6th ed. — Columbia University Press. 2007. Retrieved 2008-04-20. 
  4. "Tyrosine". Online Etymology Dictionary. 2001. 
  5. "Amino Acids - Tyrosine". 
  6. "Aromatic amino acid requirements in healthy human subjects". The Journal of Nutrition 137 (6 Suppl 1): 1576S-1578S; discussion 1597S-1598S. June 2007. doi:10.1093/jn/137.6.1576S. PMID 17513429. 
  7. "Tyrosine". University of Maryland Medical Center. 
  8. 8.0 8.1 Top 10 Foods Highest in Tyrosine
  9. "Detection and purification of tyrosine-sulfated proteins using a novel anti-sulfotyrosine monoclonal antibody". The Journal of Biological Chemistry 281 (49): 37877–87. December 2006. doi:10.1074/jbc.M609398200. PMID 17046811. 
  10. "Focus on molecules: sulfotyrosine". Experimental Eye Research 105: 85–6. December 2012. doi:10.1016/j.exer.2012.02.014. PMID 22406006. 
  11. "A renaissance in trace amines inspired by a novel GPCR family". Trends Pharmacol. Sci. 26 (5): 274–281. May 2005. doi:10.1016/ PMID 15860375. 
  12. "The endogenous substrates of brain CYP2D". Eur. J. Pharmacol. 724: 211–218. February 2014. doi:10.1016/j.ejphar.2013.12.025. PMID 24374199. 
  13. Battersby, A. R.; Binks, R.; Harper, B. J. T. (1962-01-01). "692. Alkaloid biosynthesis. Part II. The biosynthesis of morphine" (in en). Journal of the Chemical Society (Resumed): 3534–3544. doi:10.1039/JR9620003534. ISSN 0368-1769. 
  14. "The Incidence of Transient Neonatal Tyrosinemia Within a Mexican Population". Journal of Inborn Errors of Metabolism and Screening 5: 232640981774423. 27 November 2017. doi:10.1177/2326409817744230. 
  15. "Urinary phenolic acid metabolities of tyrosine". Journal of Biological Chemistry 235 (9): 2649–2652. 1960. doi:10.1016/S0021-9258(19)76930-0. 
  16. "Urinary ortho-tyrosine excretion in diabetes mellitus and renal failure: evidence for hydroxyl radical production". Kidney International 68 (5): 2281–7. November 2005. doi:10.1111/j.1523-1755.2005.00687.x. PMID 16221230. 
  17. "Accumulation of the hydroxyl free radical markers meta-, ortho-tyrosine and DOPA in cataractous lenses is accompanied by a lower protein and phenylalanine content of the water-soluble phase". Free Radical Research 39 (12): 1359–66. December 2005. doi:10.1080/10715760500307107. PMID 16298866. 
  18. "Optimized Synthesis of L-m-Tyrosine Suitable for Chemical Scale-Up". Organic Process Research & Development 11 (6): 1069–1075. 2007. doi:10.1021/op700093y. 
  19. "Effects of tyrosine and tryptophan ingestion on plasma catecholamine and 3,4-dihydroxyphenylacetic acid concentrations". The Journal of Clinical Endocrinology and Metabolism 57 (4): 760–3. October 1983. doi:10.1210/jcem-57-4-760. PMID 6885965. 
  20. "Diet-induced mood changes in normal populations". Journal of Psychiatric Research 17 (2): 147–54. 1982. doi:10.1016/0022-3956(82)90016-4. PMID 6764931. 
  21. 21.0 21.1 "Effect of tyrosine on cognitive function and blood pressure under stress". Brain Research Bulletin 33 (3): 319–23. 1994. doi:10.1016/0361-9230(94)90200-3. PMID 8293316. 
  22. "The effects of dietary neurotransmitter precursors on human behavior". The American Journal of Clinical Nutrition 42 (2): 366–70. August 1985. doi:10.1093/ajcn/42.2.366. PMID 4025206. 
  23. "Tyrosine improves behavioral and neurochemical deficits caused by cold exposure". Physiology & Behaviour. 2001. 
  24. 24.0 24.1 "Separation-induced body weight loss, impairment in alternation behavior, and autonomic tone: effects of tyrosine". Pharmacology, Biochemistry, and Behavior 68 (2): 273–81. February 2001. doi:10.1016/S0091-3057(00)00448-2. PMID 11267632. 
  25. "Effects of tyrosine, phentermine, caffeine D-amphetamine, and placebo on cognitive and motor performance deficits during sleep deprivation". Nutritional Neuroscience 6 (4): 237–46. August 2003. doi:10.1080/1028415031000120552. PMID 12887140. 
  26. "The effects of tyrosine on cognitive performance during extended wakefulness". Aviation, Space, and Environmental Medicine 66 (4): 313–9. April 1995. PMID 7794222. 
  27. "Dietary tyrosine suppresses the rise in plasma corticosterone following acute stress in rats". Life Sciences 37 (23): 2157–63. December 1985. doi:10.1016/0024-3205(85)90566-1. PMID 4068899. 
  28. "Tyrosine improves cognitive performance and reduces blood pressure in cadets after one week of a combat training course". Brain Research Bulletin 48 (2): 203–9. January 1999. doi:10.1016/S0361-9230(98)00163-4. PMID 10230711. 
  29. "Tyrosine supplementation mitigates working memory decrements during cold exposure". Physiology & Behavior 92 (4): 575–82. November 2007. doi:10.1016/j.physbeh.2007.05.003. PMID 17585971. 
  30. "Effects of L-tyrosine and carbohydrate ingestion on endurance exercise performance". Journal of Applied Physiology 93 (5): 1590–7. November 2002. doi:10.1152/japplphysiol.00625.2001. PMID 12381742. 
  31. "Influence of paroxetine, branched-chain amino acids and tyrosine on neuroendocrine system responses and fatigue in humans". Hormone and Metabolic Research 30 (4): 188–94. April 1998. doi:10.1055/s-2007-978864. PMID 9623632. 
  32. "Tyrosine improves working memory in a multitasking environment". Pharmacology, Biochemistry, and Behavior 64 (3): 495–500. November 1999. doi:10.1016/S0091-3057(99)00094-5. PMID 10548261. 
  33. "Tyrosine: Benefits, Side Effects and Dosage" (in en). 1 February 2018. 
  34. 34.0 34.1 "Perspectives of biotechnological production of L-tyrosine and its applications". Applied Microbiology and Biotechnology 77 (4): 751–62. December 2007. doi:10.1007/s00253-007-1243-y. PMID 17968539. 
  35. "Biotechnological production of L-tyrosine and derived compounds". Process Biochemistry 47 (7): 1017–1026. 2012. doi:10.1016/j.procbio.2012.04.005. 

External links


| name = Neurotransmitter metabolism intermediates
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