The AtlasAmino acidsAromatic
TyrosineTyr · Y
Phenylalanine with one oxygen added, and the raw material for dopamine, adrenaline, thyroid hormone and the pigment in skin.
Molecule · Tyr · 13 heavy atoms
Tyrosine
C9H11NO3181.19 g/mol
Phenylalanine with one oxygen added, and the raw material for dopamine, adrenaline, thyroid hormone and the pigment in skin.
Built fromthe charted ones open their own entry
- Codes
- Tyr · Y
- Formula
- C9H11NO3
- Molar mass
- 181.19 g/mol
- Systematic name
- (2S)-2-amino-3-(4-hydroxyphenyl)propanoic acid
- Side chain
- 4-Hydroxybenzyl: a phenol ring on one carbon; aromatic, weakly polar, ionises only above pH 10.
- Class
- Aromatic
- In the diet
- Conditionally essential
- Carbon skeleton
- Glucogenic and ketogenic
- pKa
- α-COOH 2.20 · α-NH3+ 9.11 · side chain 10.07
- Isoelectric point
- pH 5.66
- Hydropathy
- -1.3 (Kyte–Doolittle)
- Codons
UAUUAC- Main transporters
- SLC7A5 (LAT1, with CD98), SLC6A19 (B0AT1)
pKa and isoelectric point: Nelson and Cox, Lehninger Principles of Biochemistry, table of amino acid properties (free amino acid, 25 °C). Hydropathy: Kyte and Doolittle, J Mol Biol 1982. Essentiality: Reeds, J Nutr 2000. Formula and mass computed from the structure.
In brief
What it is
Phenylalanine with a hydroxyl group on the far end of its ring, a phenol. The body makes it from phenylalanine, so it is needed in the diet only when that conversion fails 1,2.
Why it matters
It is the starting point for the catecholamines, dopamine, noradrenaline and adrenaline, through tyrosine hydroxylase; for the thyroid hormones, built on tyrosines in thyroglobulin; and for melanin 3,4,5. Phosphorylating tyrosine on proteins is also one of the cell’s main signalling switches 6.
Where it runs short
In phenylketonuria tyrosine can no longer be made from phenylalanine, so it becomes essential and has to be supplied 2,7.
Where it turns
When its breakdown is blocked, tyrosine or its products accumulate: liver failure in tyrosinaemia type I, eye and skin lesions in type II, and dark pigment in cartilage in alkaptonuria 8,9,10.
Every disease on this page is a blockage at one step of a single pathway.
The molecule
Tyrosine is phenylalanine with a hydroxyl group at the far end of the ring, which makes the ring a phenol. The hydroxyl gives a protein a site for a hydrogen bond, for iodine and for phosphate, all three of which the body uses 4,6.
The phenol is a very weak acid. Its pKa is about 10, so at the pH of blood it is uncharged and tyrosine counts as an aromatic, slightly polar amino acid rather than a charged one.
Move across the chart to read the charge at any pH.
Computed from its pKa values (α-carboxyl 2.20, α-amino 9.11, side chain 10.07) by the Henderson–Hasselbalch equation, for the free amino acid in water at 25 °C. Inside a folded protein the same groups can shift by a unit or more. The faint lines are the other amino acids.
Kyte–Doolittle hydropathy index: positive values avoid water and tend to be buried inside a folded protein, negative values sit on its surface. Each letter is an amino acid; choose one to open it.
| 1st ↓ 2nd → | U | C | A | G | 3rd |
|---|---|---|---|---|---|
| U | UUUPhe | UCUSer | UAUTyr | UGUCys | U |
| UUCPhe | UCCSer | UACTyr | UGCCys | C | |
| UUALeu | UCASer | UAAStop | UGAStop | A | |
| UUGLeu | UCGSer | UAGStop | UGGTrp | G | |
| C | CUULeu | CCUPro | CAUHis | CGUArg | U |
| CUCLeu | CCCPro | CACHis | CGCArg | C | |
| CUALeu | CCAPro | CAAGln | CGAArg | A | |
| CUGLeu | CCGPro | CAGGln | CGGArg | G | |
| A | AUUIle | ACUThr | AAUAsn | AGUSer | U |
| AUCIle | ACCThr | AACAsn | AGCSer | C | |
| AUAIle | ACAThr | AAALys | AGAArg | A | |
| AUGMet | ACGThr | AAGLys | AGGArg | G | |
| G | GUUVal | GCUAla | GAUAsp | GGUGly | U |
| GUCVal | GCCAla | GACAsp | GGCGly | C | |
| GUAVal | GCAAla | GAAGlu | GGAGly | A | |
| GUGVal | GCGAla | GAGGlu | GGGGly | G |
Where it comes from
The body makes tyrosine from phenylalanine, in one step, by phenylalanine hydroxylase with tetrahydrobiopterin as cofactor 2,11. That makes it conditionally essential: dispensable in a normal diet, essential in phenylketonuria 7.
Requirements for the two aromatic amino acids are set together, at 25 mg per kilogram a day 12.
Conditionally essentialMade from phenylalanine by phenylalanine hydroxylase, so not needed in the diet unless that enzyme fails; requirements are set for the two together, 25 mg per kilogram a day 2,12. In adult men given a fixed phenylalanine intake, the tyrosine requirement was about 6 mg/kg a day 1.
How much
With phenylalanine, 25 mg per kilogram a day for adults 12.
In the bottle · fermentedCommercial tyrosine is made by fermentation in engineered Escherichia coli or Corynebacterium glutamicum through the shikimate pathway 13. The product is identical to the tyrosine in food.
What the body does with it
Tyrosine hydroxylase turns tyrosine into L-DOPA, which is decarboxylated to dopamine; in some cells dopamine is hydroxylated to noradrenaline and that is methylated to adrenaline 14. Most catecholamine breakdown happens inside the same cells that make them, as transmitter leaks from storage vesicles into the cytoplasm, and the adrenal medulla is the largest source of the metanephrines measured to detect a phaeochromocytoma 14.
In the thyroid, tyrosine is not used free. Tyrosine residues within thyroglobulin are iodinated and coupled while still part of that protein, and the hormones are cut out of it afterwards 4. Mutations in the thyroglobulin gene are a cause of congenital hypothyroidism 4.
In melanocytes, tyrosinase oxidises tyrosine in the first and rate-limiting step of melanin synthesis; defects in the gene cause the commonest form of oculocutaneous albinism 5.
In three sentences each
The rate-limiting step for catecholamines
Tyrosine hydroxylase converts tyrosine to L-DOPA, the step that sets how fast dopamine, noradrenaline and adrenaline are made; children who lack it have too little of all three in the brain 2,3.
Iodinated in thyroglobulin
The thyroid iodinates tyrosine residues on thyroglobulin to make mono- and diiodotyrosine; two diiodotyrosines couple to make T4, and a mono- with a diiodotyrosine makes T3 4.
A phosphate switch
In 1980 the cancer-causing protein of Rous sarcoma virus was found to add phosphate to tyrosine, a kind of protein kinase no one had seen before; tyrosine phosphorylation is now known as a central signal for growth 6.
How it is made, moved and broken down
Tyrosine’s breakdown runs through five enzymes in the liver. Each has its own disease, which is what makes the pathway so well known: tyrosine aminotransferase (tyrosinaemia type II), 4-hydroxyphenylpyruvate dioxygenase (the target of nitisinone), homogentisate dioxygenase (alkaptonuria) and fumarylacetoacetate hydrolase (tyrosinaemia type I) 8,9,10,15. The last step yields fumarate and acetoacetate 16.
Carbon skeleton · glucogenic and ketogenicBroken down to fumarate, which can make glucose, and acetoacetate, a ketone body 16.
- Tyrosine
- Tyrosine hydroxylaseTH · BH4, iron
- L-DOPA
- Aromatic L-amino acid decarboxylaseDDC · vitamin B6
- Dopamine
- Dopamine β-hydroxylaseDBH · vitamin C, copper
- Noradrenaline
- Phenylethanolamine N-methyltransferasePNMT · SAM
- Adrenaline
- Tyrosine
- Tyrosine aminotransferaseTAT · vitamin B6
- 4-Hydroxyphenylpyruvate
- 4-Hydroxyphenylpyruvate dioxygenaseHPD · iron, O₂
- Homogentisate
- Homogentisate 1,2-dioxygenaseHGD · iron, O₂
- Maleylacetoacetate
- Maleylacetoacetate isomeraseGSTZ1 · glutathione
- Fumarylacetoacetate
- Fumarylacetoacetate hydrolaseFAH
- Fumarate + acetoacetate
- Tyrosines in thyroglobulin
- Thyroid peroxidaseTPO · iodide
- MIT and DIT
- Thyroid peroxidase (coupling)TPO
- T4, or T3
Where it matters most
- Brain
- Dopamine and noradrenaline neurons; tyrosine hydroxylase deficiency causes an infantile movement disorder treatable with L-DOPA 3.
- Adrenal medulla
- Makes adrenaline and is the largest source of circulating metanephrines 14.
- Thyroid
- Builds T4 and T3 on the tyrosines of thyroglobulin 4.
- Skin, hair and eyes
- Melanocytes make melanin from tyrosine through tyrosinase 5.
- Liver
- Breaks tyrosine down; failure of the last step causes liver failure and cancer risk in tyrosinaemia type I 8.
When it goes wrong
Inherited
Tyrosinaemia type I
FAH · autosomal recessive
Liver failure with kidney and nerve involvement and a long-term risk of liver cancer 8. Nitisinone, which blocks the pathway upstream so the toxic products are never made, brought succinylacetone down to the detection limit in the first five patients treated, reported in 1992; identified early and treated, most infants stay well 8,15.
How it is foundSuccinylacetone in the newborn blood spot, then in plasma and urine 8.
Inherited
Tyrosinaemia type II (Richner–Hanhart syndrome)
TAT · autosomal recessive
Very rare. Painful thickening of the skin of the palms and soles, a keratitis that can be mistaken for herpes, and sometimes mild developmental delay; treated by restricting protein 9.
How it is foundPlasma tyrosine and TAT sequencing 9.
Inherited
Alkaptonuria
HGD · autosomal recessive
Ultra-rare. Homogentisic acid accumulates and from the third decade deposits as a bluish-black pigment in cartilage and connective tissue, ochronosis, with destructive arthritis of the spine and large joints 10,20. Nitisinone lowered urinary homogentisic acid by 99.7% in the SONIA 2 trial and in June 2025 became the first treatment approved by the FDA for the disease 21,22.
How it is foundUrine homogentisic acid; HGD genetic testing 10,21.
Inherited
Tyrosine hydroxylase deficiency
TH · autosomal recessive
Fewer than 40 cases had been reported by 2010. An infantile movement disorder, or in its severe form a neonatal encephalopathy, from too little dopamine and noradrenaline in the brain; L-DOPA treats it 3.
How it is foundLow homovanillic acid and MHPG with normal 5-HIAA in cerebrospinal fluid; TH sequencing 3.
Inherited
Oculocutaneous albinism type 1
TYR · autosomal recessive
Loss of tyrosinase, the first enzyme of melanin synthesis; the commonest form of albinism in people of European ancestry, though a quarter or more of cases remain genetically unexplained 5.
How it is foundGenetic testing of TYR 5.
How it is measured
Tyrosine is measured with phenylalanine in plasma and dried blood spots, and the two sample types differ: in one comparison plasma tyrosine read about 6 µmol/L higher than the spot 23. For the tyrosine disorders the more useful markers are the ones downstream, succinylacetone and homogentisic acid 8,21.
- Newborn tyrosine and succinylacetoneBoth are measured in the heel-prick blood spot 24.Succinylacetone is the better screen for tyrosinaemia type I than tyrosine itself 8.Tyrosine is often raised for a while in healthy newborns, especially preterm babies, so it needs separate cut-offs; measuring succinylacetone at the same time distinguishes the transient rise from the disease 24.
- Plasma tyrosine on nitisinoneMonitored in everyone taking nitisinone, which blocks the pathway below tyrosine 8,25.In alkaptonuria trials, nitisinone raised plasma tyrosine by about 700 µmol/L on average 25.The long-term consequences of that rise remain uncertain 10.
- Urine homogentisic acidThe diagnostic and treatment marker for alkaptonuria 21.Fell by 99.7% at 12 months on nitisinone in a randomised trial 21.
Food, supplements and the evidence
Establishedreplicated in people, for a named outcome
Uncertainsmall, short, mixed, surrogate or preclinical
- Tyrosine for thinking under acute stress. Small crossover trials found benefits on working memory and vigilance during cold, noise, hypoxia or a night without sleep, lasting a few hours, at doses of 100 to 300 mg per kilogram 26,27,28,29,30.
- Reviews conclude it may help only when catecholamines are temporarily depleted, with a weak recommendation at most for cognition under stress and none for physical performance 31,32.
What is strange about it
Nitisinone began as a weed killer. Chemists working from leptospermone, a natural herbicide, made a family of triketones; one of them, NTBC, damaged the corneas of rats and dogs because it blocked tyrosine breakdown, and that same action turned it into the treatment for tyrosinaemia type I 15,33.
Alkaptonuria was the disease Archibald Garrod used in 1902 to propose “chemical individuality,” the idea of inborn errors of metabolism; the urine darkens on standing because homogentisic acid oxidises 10,34.
Before nitisinone, the only effective treatment for tyrosinaemia type I was a liver transplant 15.
Where it connects
Topics on the map
On the map
A star in Conditional amino acids, one of 14. Precursor to dopamine, noradrenaline and thyroid hormone. The trials that find an effect are almost all under acute stress — cold, noise, sleep loss.
Sources
34 sources, numbered as they are cited. Every one was checked against PubMed or its publisher before it was cited here; the note under each says what it shows and what it does not.
- 1Roberts SA, Thorpe JM, Ball RO, Pencharz PB. Tyrosine requirement of healthy men receiving a fixed phenylalanine intake determined by using indicator amino acid oxidation.doi:10.1093/ajcn/73.2.276 · PMID 11157324
Six men; mean tyrosine requirement 6.0 mg/kg/day, safe 7.0.
- 2Fitzpatrick PF. Structural insights into the regulation of aromatic amino acid hydroxylation.doi:10.1016/j.sbi.2015.07.004 · PMID 26241318
PAH, TH and TPH and how each is regulated.
- 3Willemsen MA, Verbeek MM, Kamsteeg EJ, et al. Tyrosine hydroxylase deficiency: a treatable disorder of brain catecholamine biosynthesis.doi:10.1093/brain/awq087 · PMID 20430833
36 patients; two phenotypes; L-DOPA treatment.
- 4Citterio CE, Targovnik HM, Arvan P. The role of thyroglobulin in thyroid hormonogenesis.doi:10.1038/s41574-019-0184-8 · PMID 30886364
MIT and DIT on thyroglobulin tyrosines; coupling to T4 and T3.
- 5Lin S, Sanchez-Bretaño A, Leslie JS, et al. Evidence that the Ser192Tyr/Arg402Gln in cis tyrosinase gene haplotype is a disease-causing allele in oculocutaneous albinism type 1B (OCA1B).doi:10.1038/s41525-021-00275-9 · PMID 35027574
Tyrosinase as the rate-limiting enzyme of melanin; OCA1 and its missing heritability.
- 6Hunter T, Sefton BM. Transforming gene product of Rous sarcoma virus phosphorylates tyrosine.doi:10.1073/pnas.77.3.1311 · PMID 6246487
The discovery of tyrosine phosphorylation.
- 7van Spronsen FJ, Blau N, Harding C, et al. Phenylketonuria.doi:10.1038/s41572-021-00267-0 · PMID 34017006
Review of PKU and its treatment.
- 8Chinsky JM, Singh R, Ficicioglu C, et al. Diagnosis and treatment of tyrosinemia type I: a US and Canadian consensus group review and recommendations.doi:10.1038/gim.2017.101 · PMID 28771246
Succinylacetone screening; nitisinone and diet; liver cancer risk.
- 9Bouyacoub Y, Zribi H, Azzouz H, et al. Novel and recurrent mutations in the TAT gene in Tunisian families affected with Richner–Hanhart syndrome.doi:10.1016/j.gene.2013.07.066 · PMID 23954227
Tyrosinaemia type II: features and genetics.
- 10Davison AS, Norman BP. Alkaptonuria: past, present and future.doi:10.1016/bs.acc.2023.02.005 · PMID 37268334
Review; uncertainty about the hypertyrosinaemia nitisinone causes.
- 11Blau N. Sepiapterin: from sapropterin to next-generation therapy.doi:10.1016/j.ymgme.2026.110110 · PMID 42119485
BH4 as the hydroxylases’ cofactor.
- 12Joint WHO/FAO/UNU Expert Consultation. Protein and amino acid requirements in human nutrition.PMID 18330140
Phenylalanine plus tyrosine, 25 mg/kg/day.
- 13Hirasawa T, Satoh Y, Koma D. Production of aromatic amino acids and their derivatives by Escherichia coli and Corynebacterium glutamicum.doi:10.1007/s11274-025-04264-3 · PMID 39915353
Fermentation through the shikimate pathway.
- 14Eisenhofer G, Kopin IJ, Goldstein DS. Catecholamine metabolism: a contemporary view with implications for physiology and medicine.doi:10.1124/pr.56.3.1 · PMID 15317907
Synthesis and breakdown of catecholamines; the adrenal medulla and metanephrines.
- 15Lindstedt S, Holme E, Lock EA, et al. Treatment of hereditary tyrosinaemia type I by inhibition of 4-hydroxyphenylpyruvate dioxygenase.doi:10.1016/0140-6736(92)92685-9 · PMID 1383656
Five patients treated with NTBC; liver transplant had been the only treatment.
- 16Han C, Ren C, Zhi T, et al. Disruption of fumarylacetoacetate hydrolase causes spontaneous cell death under short-day conditions in Arabidopsis.doi:10.1104/pp.113.216804 · PMID 23743712
Cited for the last step of tyrosine breakdown, to fumarate and acetoacetate.
- 17Scalise M, Galluccio M, Console L, et al. The human SLC7A5 (LAT1): the intriguing histidine/large neutral amino acid transporter and its relevance to human health.doi:10.3389/fchem.2018.00243 · PMID 29988369
LAT1 at the placenta and blood–brain barrier.
- 18Lu X. The role of large neutral amino acid transporter (LAT1) in cancer.doi:10.2174/1568009619666190802135714 · PMID 31376820
LAT1 carries thyroid hormones and drugs including L-DOPA across the blood–brain barrier.
- 19Kleta R, Romeo E, Ristic Z, et al. Mutations in SLC6A19, encoding B0AT1, cause Hartnup disorder.doi:10.1038/ng1405 · PMID 15286787
Neutral amino acid transport in gut and kidney.
- 20Salem KH, Elmoghazy AD. Ochronotic arthropathy: skeletal manifestations and orthopaedic treatment.doi:10.1530/EOR-2023-0112 · PMID 40071956
The skeletal disease of alkaptonuria.
- 21Ranganath LR, Psarelli EE, Arnoux JB, et al. Efficacy and safety of once-daily nitisinone for patients with alkaptonuria (SONIA 2): an international, multicentre, open-label, randomised controlled trial.doi:10.1016/S2213-8587(20)30228-X · PMID 32822600
138 patients; urinary homogentisic acid −99.7% at 12 months.
- 22Chandani HK, Hujjat SFZ, Chandani DK, et al. Harliku (nitisinone): first FDA-approved disease-modifying therapy for alkaptonuria.doi:10.1097/MS9.0000000000004033 · PMID 41377225
Editorial on the June 2025 approval.
- 23van Vliet K, van Ginkel WG, van Dam E, et al. Dried blood spot versus venous blood sampling for phenylalanine and tyrosine.doi:10.1186/s13023-020-1343-7 · PMID 32245393
Plasma tyrosine about 6.4 µmol/L above the blood spot.
- 24Lee B, Heo WY, Kim JA, et al. Comprehensive evaluation of the NeoBase 2 non-derivatized MSMS assay and exploration of analytes with significantly different concentrations between term and preterm neonates.doi:10.3343/alm.2023.43.2.153 · PMID 36281509
Preterm cut-offs for tyrosine; succinylacetone separates transient tyrosinaemia.
- 25Mayrink FD, Dorneles G, da Silva IM, Areda CA. Efficacy and safety of nitisinone for patients with alkaptonuria: a systematic review with metanalysis.doi:10.1016/j.ymgme.2025.109099 · PMID 40157162
Three studies, 218 patients; tyrosine up by a mean 709 µmol/L.
- 26Banderet LE, Lieberman HR. Treatment with tyrosine, a neurotransmitter precursor, reduces environmental stress in humans.doi:10.1016/0361-9230(89)90096-8 · PMID 2736402
100 mg/kg; cold and hypoxia; crossover.
- 27Shurtleff D, Thomas JR, Schrot J, et al. Tyrosine reverses a cold-induced working memory deficit in humans.doi:10.1016/0091-3057(94)90299-2 · PMID 8029265
Eight men at 4 °C; no effect at room temperature.
- 28Deijen JB, Orlebeke JF. Effect of tyrosine on cognitive function and blood pressure under stress.doi:10.1016/0361-9230(94)90200-3 · PMID 8293316
Sixteen people; 90 dB noise.
- 29Neri DF, Wiegmann D, Stanny RR, et al. The effects of tyrosine on cognitive performance during extended wakefulness.PMID 7794222
More than 24 hours awake; benefit lasted about three hours.
- 30Mahoney CR, Castellani J, Kramer FM, et al. Tyrosine supplementation mitigates working memory decrements during cold exposure.doi:10.1016/j.physbeh.2007.05.003 · PMID 17585971
Nineteen people in cold water; 300 mg/kg.
- 31Jongkees BJ, Hommel B, Kühn S, Colzato LS. Effect of tyrosine supplementation on clinical and healthy populations under stress or cognitive demands: a review.doi:10.1016/j.jpsychires.2015.08.014 · PMID 26424423
Helps only when dopamine and noradrenaline are temporarily depleted.
- 32Attipoe S, Zeno SA, Lee C, et al. Tyrosine for mitigating stress and enhancing performance in healthy adult humans, a rapid evidence assessment of the literature.doi:10.7205/MILMED-D-14-00594 · PMID 26126245
Weak recommendation for cognitive stress; none for physical performance.
- 33Lock EA. From weed killer to wonder drug.doi:10.1007/978-3-319-55780-9_16 · PMID 28755195
The herbicide origin of nitisinone.
- 34Garrod AE. The incidence of alkaptonuria: a study in chemical individuality. 1902.PMID 8784780
The founding paper of inborn errors of metabolism.
This is education, not medical advice. Nothing on this page is written with knowledge of your history, your medications or your risks, and nothing here is a dose. Do not start or stop any treatment on the basis of it — talk to your own physician. Read the full medical disclaimer.