Tyrosine

C 9
H 11
N 1
O 3

Ball-and-stick Stick Space-filling

Drag to rotate; pinch or Ctrl + scroll to zoom. Arrow keys rotate, + − zoom, R resets.

24 atoms, 24 bonds.

IUPAC name: (2S)-2-amino-3-(4-hydroxyphenyl)propanoic acid
Molar mass: 181.191(24) g/mol
Atoms: 24
SMILES: C1=CC(=CC=C1CC(C(=O)O)N)O
InChIKey: OUYCCCASQSFEME-QMMMGPOBSA-N
PubChem CID: 6057

Made of

C H N O

Structural formula of tyrosine. Each unlabelled corner is a carbon atom, and the seven hydrogens on carbon are not drawn. Wedges come toward you, hashes go back. It shows which atoms are joined to which, not the shape. The model above shows the shape.

The body makes its own tyrosine from another amino acid, phenylalanine, according to the US National Cancer Institute (NCI) Thesaurus. People with phenylketonuria (PKU) lack the enzyme for that conversion, and for them NCI counts tyrosine as an essential nutrient. ChEBI, the Chemical Entities of Biological Interest database, lists it among the proteinogenic amino acids, those that cells build into proteins. NCI calls it aromatic: it is built around a benzene-like ring of six carbons.

Its formula, C₉H₁₁NO₃, joins carbon, hydrogen, nitrogen and oxygen at 181.19 g/mol. The IUPAC name, (2S)-2-amino-3-(4-hydroxyphenyl)propanoic acid, reads as a three-carbon acid with an amino group on carbon 2 and, on carbon 3, a ring bearing an –OH. The Hazardous Substances Data Bank (HSDB) describes white crystals in fine, silky needles. Only 0.453 g dissolves in a litre of water at 25 °C, yet the solid is soluble in alkaline solution.

Structure and bonding

Tyrosine’s 24 atoms gather around a flat six-carbon ring with groups at two opposite corners. In Ball-and-stick, one corner carries the oxygen of an O–H group. The other carries a CH₂ carbon linked to a second chain carbon, which holds the amino group, –NH₂, one hydrogen and the carboxyl group, –COOH.

Turned edge-on, the ring, its O–H and the CH₂ carbon share one plane, and the second chain carbon rises out of it to one side with its groups. Space-filling swells this into a flat plate with a crowded head. With Labels on, O marks the three oxygens: one on the ring, two on the carboxyl carbon.

The ring is drawn with three double bonds alternating with three single ones. Yet in this computed model all six ring bonds measure 1.385 to 1.395 Å, while the carboxyl C=O and C–O stay distinct at 1.224 and 1.358 Å. Chem1’s term for this is a conjugated system: the double-bond electrons belong to the whole ring rather than to three fixed bonds, as in benzene. The model draws the uncharged molecule; which charged forms an amino acid can take is the subject of the glycine page.

Where it turns up

Mushrooms and potatoes hold enough tyrosine to cause colour problems for the food industry, according to HSDB. The cause is polyphenol oxidases, enzymes also called tyrosinase, which occur widely in plants. Many of them oxidise tyrosine, and the products link up into polymers that HSDB calls grey-black colour bodies. Tyrosine is also present, at varying concentrations, through the stages of bread production. Some plants turn it into other compounds: sugar cane makes p-coumaric acid from it, and daffodils make narwedine.

Manufacturers isolate it from silk waste, from casein or from corn, according to HSDB. Reports to the US Environmental Protection Agency (EPA) put the national volume for 2023 at 50,000 to under 250,000 pounds, the same band as in each year from 2020. Haz-Map, an occupational-health database, records its use in biochemical research.

Why it matters

In melanocytes, specialised cells that produce the pigment melanin, the enzyme tyrosinase takes the first step, converting tyrosine to dopaquinone, according to MedlinePlus Genetics. Further reactions carry dopaquinone on to melanin in skin, hair follicles, the iris and the retina. Medical Subject Headings (MeSH) describes tyrosinase as a copper protein, and melanins as insoluble polymers of tyrosine derivatives that darken skin and hair and protect against sunburn. Most mutations in TYR, the tyrosinase gene, abolish the enzyme’s activity, so melanocytes make no melanin: oculocutaneous albinism type 1A, with white hair, light-coloured eyes and very pale skin.

NCI also lists tyrosine as the precursor, the starting material, of catecholamines and thyroxine, and MeSH names epinephrine and the thyroid hormones. Tyrosine hydroxylase converts it to L-DOPA, according to MedlinePlus Genetics; the steps beyond belong to the dopamine page, and the thyroid hormones to iodine. Inside proteins, tyrosine kinases attach phosphate groups to tyrosine units, on MeSH’s definition. They take part in cell signalling, growth and division, and some drugs that block them, tyrosine kinase inhibitors, treat cancer, according to the NCI.

Properties

Properties of tyrosine Molar mass summed from IUPAC/CIAAW 2024 standard atomic weights; formula, atom and bond counts and PubChem's molecular weight from PubChem CID 6057.
Property	Value	Unit	Source
Molecular formula (Hill order)	C₉H₁₁NO₃
Molar mass	181.191(24) g/mol	g/mol	IUPAC/CIAAW 2024
Carbon atoms	9
Hydrogen atoms	11
Nitrogen atoms	1
Oxygen atoms	3
Bonds	24
Single bonds	20
Double bonds	4
PubChem molecular weight	181.19 g/mol	g/mol	PubChem

Safety

Most reports on pure tyrosine find no hazard to classify: 226 of 268, or 84.3%, say it meets no Globally Harmonized System (GHS) criterion. A minority give the signal word Warning, with skin irritation, serious eye irritation and possible respiratory irritation as the hazards. Haz-Map records it as safe when used as a flavouring in food. Each classification is listed in the PubChem Laboratory Chemical Safety Summary for tyrosine.

Questions

Which atom separates tyrosine from phenylalanine?

One oxygen atom. Both are three-carbon acids with an amino group on carbon 2 and a six-carbon ring on carbon 3. Tyrosine's ring carries an –OH at the corner opposite the chain, in place of a ring hydrogen. That makes tyrosine C₉H₁₁NO₃, 181.19 g/mol, and phenylalanine C₉H₁₁NO₂, 165.19 g/mol, with eleven hydrogens each. Their computed 3D models hold 24 and 23 atoms.

What are the pK values of tyrosine?

HSDB gives three pK values, each the negative logarithm of a dissociation constant. They are 2.20 for the carboxylic acid, –COOH; 9.11 for the amino group, –NH₂; and 10.07 for the phenol, the –OH fixed to the ring. The 3D model draws all three uncharged: the carboxyl carbon carries a C=O and a C–O–H, the nitrogen two hydrogens and the ring oxygen one.

What is tyrosinaemia?

It is a genetic disorder that hampers the breakdown of tyrosine, according to MedlinePlus Genetics. A faulty FAH, TAT or HPD gene weakens one of the liver enzymes that break it down, so tyrosine and its byproducts pile up to toxic levels. Type I occurs in about 1 in 100,000 people worldwide. About 1 in 10 newborns briefly have raised tyrosine, transient tyrosinaemia, which is not genetic and probably comes from vitamin C deficiency or an immature liver.

Why does urine turn dark in alkaptonuria?

In alkaptonuria the enzyme homogentisate 1,2-dioxygenase works poorly. It normally helps break down phenylalanine and tyrosine, according to MedlinePlus Genetics. HSDB traces tyrosine's breakdown through p-hydroxyphenylpyruvic acid, which loses carbon dioxide to become homogentisic acid, and on to fumarate and acetoacetate. Without a working enzyme, homogentisic acid collects in the body. The surplus leaves in the urine, and that urine darkens once air reaches it.

Made of the same elements

C₉H₁₁NO₂ Phenylalanine 23 atoms, 23 bonds.
C₈H₁₁NO₂ Dopamine 22 atoms, 22 bonds.
C₉H₁₃NO₃ Epinephrine 26 atoms, 26 bonds.
C₈H₉NO₂ Acetaminophen 20 atoms, 20 bonds.
C₁₀H₁₂N₂O Serotonin 25 atoms, 26 bonds.
C₁₁H₁₂N₂O₂ Tryptophan 27 atoms, 28 bonds.
C₈H₁₀N₄O₂ Caffeine 24 atoms, 25 bonds.
C₆H₁₃NO₂ Isoleucine 22 atoms, 21 bonds.

All 25 compounds made of carbon, hydrogen, nitrogen and oxygen

C₆H₁₃NO₂ Leucine 22 atoms, 21 bonds.
C₅H₉NO₄ Glutamic acid 19 atoms, 18 bonds.
C₃H₇NO₂ Alanine 13 atoms, 12 bonds.
C₁₂H₁₇NO DEET 31 atoms, 31 bonds.
C₁₃H₁₆N₂O₂ Melatonin 33 atoms, 34 bonds.
C₅H₆N₂O₂ Thymine 15 atoms, 15 bonds.
C₁₃H₂₁NO₃ Albuterol 38 atoms, 38 bonds.
C₂H₅NO₂ Glycine 10 atoms, 9 bonds.
C₄H₄N₂O₂ Uracil 12 atoms, 12 bonds.
C₅H₄N₄O₃ Uric acid 16 atoms, 17 bonds.
C₁₄H₁₈N₂O₅ Aspartame 39 atoms, 39 bonds.
C₄H₅N₃O Cytosine 13 atoms, 13 bonds.
C₅H₅N₅O Guanine 16 atoms, 17 bonds.
CO(NH₂)₂ Urea 8 atoms, 7 bonds.
C₁₄H₂₂N₂O Lidocaine 39 atoms, 39 bonds.
C₁₇H₂₁NO Diphenhydramine 40 atoms, 41 bonds.
C₂₀H₂₄N₂O₂ Quinine 48 atoms, 51 bonds.