# Tyrosine
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{{Short description|Amino acid}}
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{{Chembox
| ImageFile = L-Tyrosin - L-Tyrosine.svg
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| ImageCaption = [Skeletal formula](/source/Skeletal_formula) of L-tyrosine
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| ImageName = Skeletal formula of the L-isomer
| ImageFile1 = L-Tyrosin phys.svg
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| ImageCaption1 = L-Tyrosine at physiological pH
| ImageFileL2 = File:Tyrosine-from-xtal-3D-bs-17.png
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| ImageCaptionL2 = [ball-and-stick model](/source/ball-and-stick_model)[{{ cite journal | vauthors = Frey MN, Koetzle TF, Lehmann MS, Hamilton WC | title = 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 | journal = [J. Chem. Phys.](/source/The_Journal_of_Chemical_Physics) | volume = 58 | pages = 2547–2556 | year = 1973 | issue = 6 | doi = 10.1063/1.1679537 | bibcode = 1973JChPh..58.2547F }}]
| ImageFileR2 = Tyrosine-from-xtal-3D-sf.png
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| ImageCaptionR2 = [space-filling model](/source/space-filling_model)[{{cite web| url = http://www.chem.qmul.ac.uk/iupac/AminoAcid/AA1n2.html | title = Nomenclature and Symbolism for Amino Acids and Peptides | publisher = IUPAC-IUB Joint Commission on Biochemical Nomenclature | year = 1983 | access-date = 5 March 2018| archive-url= https://web.archive.org/web/20081009023202/http://www.chem.qmul.ac.uk/iupac/AminoAcid/AA1n2.html| archive-date= 9 October 2008 | url-status= live}}] or '''4-hydroxyphenylalanine''' is one of the 20 [standard amino acid](/source/standard_amino_acid)s that are used by [cells](/source/cell_(biology)) to [synthesize proteins](/source/protein_biosynthesis). It is a [conditionally essential amino acid](/source/conditionally_essential_amino_acid) with a [polar side group](/source/Proteinogenic_amino_acid). The word "tyrosine" is from the [Greek](/source/Greek_language) {{wikt-lang|grc|τυρός|tyrós}}, meaning {{gloss|[cheese](/source/cheese)}}, as it was first discovered in 1846 by German chemist [Justus von Liebig](/source/Justus_von_Liebig) in the protein [casein](/source/casein) from cheese.[{{cite encyclopedia | url = http://www.infoplease.com/ce6/sci/A0849873.html | title = Tyrosine | year = 2007 | encyclopedia = The Columbia Electronic Encyclopedia, 6th ed | publisher = Infoplease.com — Columbia University Press | access-date = 2008-04-20}}][{{cite web | url = http://www.etymonline.com/index.php?term=tyrosine | title = Tyrosine | vauthors = Harper D | year = 2001 | work = Online Etymology Dictionary | access-date = 2008-04-20}}] It is called '''tyrosyl''' when referred to as a [functional group](/source/functional_group) or side chain. While tyrosine is generally classified as a [hydrophobic](/source/Hydrophobe) amino acid, it is more hydrophilic than [phenylalanine](/source/phenylalanine).[{{Cite web|url=http://www.biology.arizona.edu/biochemistry/problem_sets/aa/Tyrosine.html|title=Amino Acids - Tyrosine|website=www.biology.arizona.edu|access-date=2018-01-31}}] It is [encoded](/source/Genetic_code) by the [codon](/source/Genetic_code)s UAC and UAU in [messenger RNA](/source/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](/source/threonine), U was avoided for its similarity with V for [valine](/source/valine), W was assigned to [tryptophan](/source/tryptophan), while X was reserved for undetermined or atypical amino acids.[{{Cite journal |date=10 July 1968 |title=IUPAC-IUB Commission on Biochemical Nomenclature A One-Letter Notation for Amino Acid Sequences |url=https://www.jbc.org/article/S0021-9258(19)34176-6/pdf |journal=Journal of Biological Chemistry |language=en |volume=243 |issue=13 |pages=3557–3559 |doi=10.1016/S0021-9258(19)34176-6|doi-access=free }}] The mnemonic t''Y''rosine was also proposed.[{{Cite journal |last=Saffran |first=M. |date=April 1998 |title=Amino acid names and parlor games: from trivial names to a one-letter code, amino acid names have strained students' memories. Is a more rational nomenclature possible? |url=http://linkinghub.elsevier.com/retrieve/pii/S0307441297001672 |journal=Biochemical Education |language=en |volume=26 |issue=2 |pages=116–118 |doi=10.1016/S0307-4412(97)00167-2|url-access=subscription }}]
==Functions==
Aside from being a [proteinogenic amino acid](/source/proteinogenic_amino_acid), tyrosine has a special role by virtue of the [phenol](/source/phenol) functionality. Its hydroxy group is able to form the [ester linkage](/source/ester_linkage), with phosphate in particular. Phosphate groups are transferred to tyrosine residues by way of [protein tyrosine kinase](/source/protein_tyrosine_kinase)s. This is one of the [post-translational modification](/source/post-translational_modification)s. Phosphorylated tyrosine occurs in proteins that are part of [signal transduction](/source/signal_transduction) processes.
Similar functionality is also presented in [serine](/source/serine) and [threonine](/source/threonine), whose side chains have a hydroxy group, but are [alcohols](/source/Alcohol_(chemistry)). Phosphorylation of these three amino acids' [moieties](/source/Moiety_(chemistry)) (including tyrosine) creates a negative charge on their ends, which is greater than the negative charge of the only negatively charged [aspartic](/source/Aspartic_acid) and [glutamic](/source/Glutamic_acid) acids. Phosphorylated proteins keep these same properties—which are useful for more reliable protein-protein interactions—by means of phosphotyrosine, [phosphoserine](/source/phosphoserine) and phosphothreonine.[{{Cite journal |last=Hunter |first=Tony |date=2012-09-19 |title=Why nature chose phosphate to modify proteins |journal=Philosophical Transactions of the Royal Society B: Biological Sciences |language=en |volume=367 |issue=1602 |pages=2513–2516 |doi=10.1098/rstb.2012.0013 |issn=0962-8436 |pmc=3415839 |pmid=22889903}}]
Binding sites for a signalling phosphoprotein may be diverse in their chemical structure.[{{Cite journal |last1=Lu |first1=Zheng-Chang |last2=Jiang |first2=Fan |last3=Wu |first3=Yun-Dong |date=2021-12-11 |title=Phosphate binding sites prediction in phosphorylation-dependent protein-protein interactions |journal=Bioinformatics |volume=37 |issue=24 |pages=4712–4718 |doi=10.1093/bioinformatics/btab525 |issn=1367-4811 |pmid=34270697}}]
Phosphorylation of the hydroxyl group can change the activity of the target protein, or may form part of a signaling cascade via [SH2 domain](/source/SH2_domain) binding.[{{Cite journal |last1=Liu |first1=Bernard A. |last2=Nash |first2=Piers D. |date=2012-09-19 |title=Evolution of SH2 domains and phosphotyrosine signalling networks |journal=Philosophical Transactions of the Royal Society B: Biological Sciences |language=en |volume=367 |issue=1602 |pages=2556–2573 |doi=10.1098/rstb.2012.0107 |issn=0962-8436 |pmc=3415846 |pmid=22889907}}]
A tyrosine residue also plays an important role in [photosynthesis](/source/photosynthesis). In [chloroplast](/source/chloroplast)s ([photosystem II](/source/photosystem_II)), it acts as an electron donor in the [reduction](/source/Redox) of oxidized [chlorophyll](/source/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](/source/Oxygen-evolving_complex).[{{Cite journal |last=Barry |first=Bridgette A. |date=January 2015 |title=Reaction dynamics and proton coupled electron transfer: studies of tyrosine-based charge transfer in natural and biomimetic systems |journal=Biochimica et Biophysica Acta (BBA) - Bioenergetics |volume=1847 |issue=1 |pages=46–54 |doi=10.1016/j.bbabio.2014.09.003 |issn=0006-3002 |pmid=25260243}}]
==Dietary requirements and sources==
The [Dietary Reference Intake](/source/Dietary_Reference_Intake) for tyrosine is usually estimated together with [phenylalanine](/source/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.[{{cite journal | vauthors = Pencharz PB, Hsu JW, Ball RO | title = Aromatic amino acid requirements in healthy human subjects | journal = The Journal of Nutrition | volume = 137 | issue = 6 Suppl 1 | pages = 1576S-1578S; discussion 1597S-1598S | date = June 2007 | pmid = 17513429 | doi = 10.1093/jn/137.6.1576S | url = https://academic.oup.com/jn/article/137/6/1576S/4664888 | doi-access = free | url-access = subscription }}]
Tyrosine, which can also be synthesized in the body from phenylalanine, is found in many high-[protein](/source/protein) food products such as [meat](/source/meat), [fish](/source/Fish_(food)), [cheese](/source/cheese), [cottage cheese](/source/cottage_cheese), [milk](/source/milk), [yogurt](/source/yogurt), [peanut](/source/peanut)s, [almond](/source/almond)s, [pumpkin seed](/source/pumpkin_seed)s, [sesame seed](/source/sesame_seed)s, [soy protein](/source/soy_products) and [lima bean](/source/lima_bean)s.[Nutient Ranking Tool. MyFoodData.com. https://tools.myfooddata.com/nutrient-ranking-tool/tyrosine/all/highest][{{cite web|title=Tyrosine|url=http://www.umm.edu/altmed/articles/tyrosine-000329.htm|work=University of Maryland Medical Center|access-date=2011-03-17|archive-date=2013-06-04|archive-url=https://web.archive.org/web/20130604003052/http://www.umm.edu/altmed/articles/tyrosine-000329.htm|url-status=dead}}] For example, the white of an egg has about 250 mg per egg,[[http://www.healthaliciousness.com/articles/high-tyrosine-foods.php Top 10 Foods Highest in Tyrosine]] while beef, lamb, pork, tuna, salmon, chicken, and turkey contain about 500–1000 mg per {{Convert|3|oz|g}} portion.[Nutient Ranking Tool. MyFoodData.com. https://tools.myfooddata.com https://tools.myfooddata.com/nutrient-ranking-tool/tyrosine/meats/highest/ounces/common/no]
== Biosynthesis ==
[[Image:Tyrosine biosynthesis.svg|thumb|center|400px|class=skin-invert-image|Plant biosynthesis of tyrosine from [prephenate](/source/prephenate).]]
In plants and most microorganisms, tyrosine is produced via [prephenate](/source/prephenic_acid), an intermediate on the [shikimate pathway](/source/shikimate_pathway). Prephenate is [oxidatively decarboxylated](/source/oxidative_decarboxylation) with retention of the [hydroxyl](/source/hydroxyl) group to give ''p''-hydroxyphenylpyruvate, which is [transaminated](/source/transamination) using [glutamate](/source/glutamic_acid) as the nitrogen source to give tyrosine and [α-ketoglutarate](/source/Alpha-Ketoglutaric_acid).
[Mammal](/source/Mammal)s synthesize tyrosine from the essential amino acid [phenylalanine](/source/phenylalanine) (Phe), which is derived from food. The conversion of Phe to Tyr is catalyzed by the [enzyme](/source/enzyme) [phenylalanine hydroxylase](/source/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](/source/phenylalanine), such that it becomes tyrosine.
==Metabolism==
center|thumb|800px|class=skin-invert-image|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](/source/phosphorylation)) by [protein kinase](/source/protein_kinase)s. 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](/source/antibody). Tyrosine residues may also be modified by the addition of a sulfate group, a process known as [tyrosine sulfation](/source/tyrosine_sulfation).[{{cite journal | vauthors = Hoffhines AJ, Damoc E, Bridges KG, Leary JA, Moore KL | title = Detection and purification of tyrosine-sulfated proteins using a novel anti-sulfotyrosine monoclonal antibody | journal = The Journal of Biological Chemistry | volume = 281 | issue = 49 | pages = 37877–87 | date = December 2006 | pmid = 17046811 | pmc = 1764208 | doi = 10.1074/jbc.M609398200 | doi-access = free }}] [Tyrosine sulfation](/source/Tyrosine_sulfation) is catalyzed by [tyrosylprotein sulfotransferase](/source/tyrosylprotein_sulfotransferase) (TPST). Like the phosphotyrosine antibodies mentioned above, antibodies have recently been described that specifically detect sulfotyrosine.[{{cite journal | vauthors = Kanan Y, Hamilton RA, Sherry DM, Al-Ubaidi MR | title = Focus on molecules: sulfotyrosine | journal = Experimental Eye Research | volume = 105 | pages = 85–6 | date = December 2012 | pmid = 22406006 | pmc = 3629733 | doi = 10.1016/j.exer.2012.02.014 }}]
===Precursor to neurotransmitters and hormones===
In dopaminergic cells in the [brain](/source/brain), tyrosine is converted to [L-DOPA](/source/L-DOPA) by the [enzyme](/source/enzyme) [tyrosine hydroxylase](/source/tyrosine_hydroxylase) (TH). TH is the [rate-limiting enzyme](/source/rate-limiting_enzyme) involved in the synthesis of the [neurotransmitter](/source/neurotransmitter) [dopamine](/source/dopamine). Dopamine can then be converted into other [catecholamine](/source/catecholamine)s, such as [norepinephrine](/source/norepinephrine) (noradrenaline) and [epinephrine](/source/epinephrine) (adrenaline).
The [thyroid](/source/thyroid) hormones [triiodothyronine](/source/triiodothyronine) (T3) and [thyroxine](/source/thyroxine) (T4) in the [colloid](/source/colloid) of the [thyroid](/source/thyroid) are also derived from tyrosine.
{{Phenylalanine biosynthesis|caption=Tyrosine is a precursor to trace amine compounds and the catecholamines.}}
=== Precursor to other compounds ===
The latex of ''[Papaver somniferum](/source/Papaver_somniferum)'', the opium poppy, has been shown to convert tyrosine into the [alkaloid](/source/alkaloid) [morphine](/source/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.[{{Cite journal |last1=Battersby |first1=A. R. |last2=Binks |first2=R. |last3=Harper |first3=B. J. T. |date=1962-01-01 |title=692. Alkaloid biosynthesis. Part II. The biosynthesis of morphine |url=https://pubs.rsc.org/en/content/articlelanding/1962/jr/jr9620003534 |journal=Journal of the Chemical Society |language=en |pages=3534–3544 |doi=10.1039/JR9620003534 |issn=0368-1769|url-access=subscription }}][Tyrosine ammonia lyase](/source/Tyrosine_ammonia_lyase) (TAL) is an enzyme in the natural phenols biosynthesis pathway. It transforms L-tyrosine into [''p''-coumaric acid](/source/p-Coumaric_acid). Tyrosine is also the precursor to the pigment ''[melanin](/source/melanin)''. Tyrosine (or its precursor phenylalanine) is needed to synthesize the benzoquinone structure which forms part of [coenzyme Q10](/source/coenzyme_Q10).[{{Cite journal |vauthors=Bentinger M, Tekle M, Dallner G |date=May 2010 |title=Coenzyme Q--biosynthesis and functions |journal=Biochemical and Biophysical Research Communications |volume=396 |issue=1 |pages=74–9 |doi=10.1016/j.bbrc.2010.02.147 |pmid=20494114 |bibcode=2010BBRC..396...74B }}][{{cite journal |doi=10.1016/j.bbabio.2016.03.036 |title=Coenzyme Q biosynthesis in health and disease |date=2016 |last1=Acosta |first1=Manuel Jesús |last2=Vazquez Fonseca |first2=Luis |last3=Desbats |first3=Maria Andrea |last4=Cerqua |first4=Cristina |last5=Zordan |first5=Roberta |last6=Trevisson |first6=Eva |last7=Salviati |first7=Leonardo |journal=Biochimica et Biophysica Acta (BBA) - Bioenergetics |volume=1857 |issue=8 |pages=1079–1085 |pmid=27060254 |doi-access=free }}]
=== Degradation ===
[[Image:Tyrosinedegradation2.png|thumb|center|750px|class=skin-invert-image|The decomposition of tyrosine to [acetoacetate](/source/acetoacetic_acid) and [fumarate](/source/fumarate). Two dioxygenases are necessary for the decomposition path. The end products can then enter into the [citric acid cycle](/source/citric_acid_cycle).]]{{citation needed|date=November 2023}}
The decomposition of L-tyrosine (syn. ''para''-hydroxyphenylalanine) begins with an α-ketoglutarate dependent [transamination](/source/transamination) through the [tyrosine transaminase](/source/tyrosine_transaminase) to [''para''-hydroxyphenylpyruvate](/source/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](/source/p-Hydroxyphenylpyruvate_dioxygenase) and splitting off CO2 [homogentisate](/source/homogentisic_acid) (2,5-dihydroxyphenyl-1-acetate).[{{cite journal | vauthors = Zea-Rey AV, Cruz-Camino H, Vazquez-Cantu DL, Gutiérrez-García VM, Santos-Guzmán J, Cantú-Reyna C |title=The Incidence of Transient Neonatal Tyrosinemia Within a Mexican Population |journal=Journal of Inborn Errors of Metabolism and Screening |date=27 November 2017 |volume=5 |pages=232640981774423 |doi=10.1177/2326409817744230|doi-access=free }}] In order to split the aromatic ring of homogentisate, a further dioxygenase, [homogentisate 1,2-dioxygenase](/source/homogentisate_1%2C2-dioxygenase) is required. Thereby, through the incorporation of a further O2 molecule, [maleylacetoacetate](/source/maleylacetoacetate) is created.
[Fumarylacetoacetate](/source/Fumarylacetoacetate) is created by [maleylacetoacetate ''cis''-''trans''-isomerase](/source/4-maleylacetoacetate_cis-trans-isomerase) through rotation of the carboxyl group created from the hydroxyl group via oxidation. This ''cis-trans''-isomerase contains [glutathione](/source/glutathione) as a [coenzyme](/source/coenzyme). Fumarylacetoacetate is finally split by the enzyme [fumarylacetoacetate hydrolase](/source/fumarylacetoacetate_hydrolase) through the addition of a water molecule.
Thereby [fumarate](/source/fumarate) (also a metabolite of the citric acid cycle) and [acetoacetate](/source/acetoacetic_acid) (3-ketobutyroate) are liberated. Acetoacetate is a [ketone body](/source/ketone_body), which is activated with succinyl-CoA, and thereafter it can be converted into [acetyl-CoA](/source/acetyl-CoA), which in turn can be oxidized by the [citric acid cycle](/source/citric_acid_cycle) or be used for [fatty acid synthesis](/source/fatty_acid_synthesis).
[Phloretic acid](/source/Phloretic_acid) is also a urinary metabolite of tyrosine in rats.[{{cite journal | vauthors = Booth AN, Masri MS, Robbins DJ, Emerson OH, Jones FT, DeEds F | year = 1960 | title = Urinary phenolic acid metabolities of tyrosine | journal = Journal of Biological Chemistry | volume = 235 | issue = 9| pages = 2649–2652 | doi = 10.1016/S0021-9258(19)76930-0 | doi-access = free }}]
==Ortho- and meta-tyrosine==
[[Image:Phe Tyr.png|thumb|right|500px|class=skin-invert-image|Enzymatic [oxidation](/source/oxidation) of tyrosine by [phenylalanine hydroxylase](/source/phenylalanine_hydroxylase) (top) and non-enyzmatic oxidation by hydroxyl [free radical](/source/free_radical)s (middle and bottom).]]
Three [structural isomers](/source/structural_isomers) of L-tyrosine are known. In addition to the common amino acid L-tyrosine, which is the [para isomer](/source/para_isomer) (''para''-tyr, ''p''-tyr or 4-hydroxyphenylalanine), there are two additional regioisomers, namely '''''meta''-tyrosine''' (also known as {{nowrap|'''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](/source/free-radical) hydroxylation of phenylalanine under conditions of [oxidative stress](/source/oxidative_stress).[{{cite journal | vauthors = Molnár GA, Wagner Z, Markó L, Kó Szegi T, Mohás M, Kocsis B, Matus Z, Wagner L, Tamaskó M, Mazák I, Laczy B, Nagy J, Wittmann I | title = Urinary ortho-tyrosine excretion in diabetes mellitus and renal failure: evidence for hydroxyl radical production | journal = Kidney International | volume = 68 | issue = 5 | pages = 2281–7 | date = November 2005 | pmid = 16221230 | doi = 10.1111/j.1523-1755.2005.00687.x | doi-access = free }}][{{cite journal | vauthors = Molnár GA, Nemes V, Biró Z, Ludány A, Wagner Z, Wittmann I | title = 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 | journal = Free Radical Research | volume = 39 | issue = 12 | pages = 1359–66 | date = December 2005 | pmid = 16298866 | doi = 10.1080/10715760500307107 | s2cid = 31154432 }}] They are toxic to both animals and plants.[{{cite journal | last1=Bertin | first1=Cécile | last2=Weston | first2=Leslie A. | last3=Huang | first3=Tengfang | last4=Jander | first4=Georg | last5=Owens | first5=Thomas | last6=Meinwald | first6=Jerrold | last7=Schroeder | first7=Frank C. | title=Grass roots chemistry: ''meta'' -Tyrosine, an herbicidal nonprotein amino acid | journal=Proceedings of the National Academy of Sciences | date=2007 | volume=104 | issue=43 | pages=16964–16969 | doi=10.1073/pnas.0707198104 | doi-access=free | pmid=17940026 | pmc=2040483 | bibcode=2007PNAS..10416964B }}][{{cite journal | last1=Ipson | first1=Brett R. | last2=Fisher | first2=Alfred L. | title=Roles of the tyrosine isomers meta- tyrosine and ortho- tyrosine in oxidative stress | journal=Ageing Research Reviews | date=2016 | volume=27 | pages=93–107 | doi=10.1016/j.arr.2016.03.005 | pmid=27039887 | pmc=4841466 }}][{{cite journal | last1=Tyminski | first1=Marcin | last2=Ciacka | first2=Katarzyna | last3=Staszek | first3=Pawel | last4=Gniazdowska | first4=Agnieszka | last5=Krasuska | first5=Urszula | title=Toxicity of meta-Tyrosine | journal=Plants | date=2021 | volume=10 | issue=12 | page=2800 | doi=10.3390/plants10122800 | doi-access=free | pmid=34961269 | pmc=8707607 | bibcode=2021Plnts..10.2800T }}]
==Medical use==
Tyrosine is a precursor to [neurotransmitter](/source/neurotransmitter)s and increases plasma neurotransmitter levels (particularly dopamine and norepinephrine),[{{cite journal | vauthors = Rasmussen DD, Ishizuka B, Quigley ME, Yen SS | title = Effects of tyrosine and tryptophan ingestion on plasma catecholamine and 3,4-dihydroxyphenylacetic acid concentrations | journal = The Journal of Clinical Endocrinology and Metabolism | volume = 57 | issue = 4 | pages = 760–3 | date = October 1983 | pmid = 6885965 | doi = 10.1210/jcem-57-4-760 }}] but has little if any effect on mood in normal subjects.[{{cite journal | vauthors = Leathwood PD, Pollet P | title = Diet-induced mood changes in normal populations | journal = Journal of Psychiatric Research | volume = 17 | issue = 2 | pages = 147–54 | year = 1982 | pmid = 6764931 | doi = 10.1016/0022-3956(82)90016-4 }}][{{cite journal | vauthors = Deijen JB, Orlebeke JF | title = Effect of tyrosine on cognitive function and blood pressure under stress | journal = Brain Research Bulletin | volume = 33 | issue = 3 | pages = 319–23 | year = 1994 | pmid = 8293316 | doi = 10.1016/0361-9230(94)90200-3 | s2cid = 33823121 }}][{{cite journal | vauthors = Lieberman HR, Corkin S, Spring BJ, Wurtman RJ, Growdon JH | title = The effects of dietary neurotransmitter precursors on human behavior | journal = The American Journal of Clinical Nutrition | volume = 42 | issue = 2 | pages = 366–70 | date = August 1985 | pmid = 4025206 | doi = 10.1093/ajcn/42.2.366 }}]
A 2015 [systematic review](/source/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](/source/cognitive_load)" and therefore "tyrosine may benefit healthy individuals exposed to demanding situational conditions".[{{cite journal |last1=Jung |first1=Sophie E |last2=Hase |first2=Adrian |last3=ann het Rot |first3=Marije |title=Behavioral and cognitive effects of tyrosine intake in healthy human adults |journal=[Pharmacology Biochemistry and Behavior](/source/Pharmacology_Biochemistry_and_Behavior) |date=2015 |volume=133 |pages=1–6 |doi=10.1016/j.pbb.2015.03.008 |pmid=25797188 |s2cid=30331663 |hdl=11370/22787e1e-591b-4b78-9d7c-dbd6f47506ca |hdl-access=free }}]
==Industrial synthesis==
L-Tyrosine is used in [pharmaceuticals](/source/pharmaceuticals), [dietary supplements](/source/dietary_supplements), and [food additives](/source/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](/source/tyrosine_phenol-lyase).[{{cite journal | vauthors = Lütke-Eversloh T, Santos CN, Stephanopoulos G | title = Perspectives of biotechnological production of L-tyrosine and its applications | journal = Applied Microbiology and Biotechnology | volume = 77 | issue = 4 | pages = 751–62 | date = December 2007 | pmid = 17968539 | doi = 10.1007/s00253-007-1243-y | s2cid = 23088822 }}] Advances in [genetic engineering](/source/genetic_engineering) and the advent of [industrial fermentation](/source/industrial_fermentation) have shifted the synthesis of L-tyrosine to the use of engineered strains of ''E. coli''.[{{cite journal | vauthors = Chavez-Bejar M, Baez-Viveros J, Martinez A, Bolivar F, Gosset G | year = 2012 | title = Biotechnological production of L-tyrosine and derived compounds | journal = Process Biochemistry | volume = 47 | issue = 7| pages = 1017–1026 | doi=10.1016/j.procbio.2012.04.005}}]