Urocanic acid

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Urocanic acid
Urocanic acid.svg
Preferred IUPAC name
(2E)-3-(1H-imidazol-4-yl)prop-2-enoic acid
Other names
(E)-3-(1H-imidazol-4-yl)acrylic acid
3D model (JSmol)
ECHA InfoCard 100.002.963
MeSH Urocanic+acid
Molar mass 138.124 g/mol
Melting point 225 °C (437 °F; 498 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Urocanic acid is an intermediate in the catabolism of L-histidine.


It is formed from L-histidine through the action of histidine ammonialyase (also known as histidase or histidinase) by elimination of ammonium.

In the liver, urocanic acid is transformed by urocanate hydratase (or urocanase) to 4-imidazolone-5-propionic acid and subsequently to glutamic acid.

Clinical significance[edit]

Inherited deficiency of urocanase leads to elevated levels of urocanic acid in the urine, a condition known as urocanic aciduria.

An important role for the onset of atopic dermatitis and asthma has been attributed to Filaggrin, a skin precursor of urocanic acid.[1][2]


Urocanic acid was detected in animal sweat and skin where, among other possible functions, it acts as an endogenous sunscreen or photoprotectant against UVB-induced DNA damage. Urocanic acid is found predominantly in the stratum corneum of the skin and it is likely that most of it is derived from filaggrin catabolism (a histidine-rich protein). When exposed to UVB irradiation, trans-urocanic acid is converted in vitro and in vivo to the cis isomer.[3] The cis form is known to activate regulatory T cells.[4]

Some studies attribute filaggrin an important role in keeping the skin surface slightly acidic, through a breaking down mechanism to form histidine and subsequently trans-urocanic acid,[5] however others have shown that the filaggrin–histidine–urocanic acid cascade is not essential for skin acidification.[6]


Urocanic acid was first isolated in 1874 by the chemist Max Jaffé from the urine of a dog,[7][8][7] hence the name (Latin: urina = urine, and canis = dog).

See also[edit]


  1. ^ Park KD, Pak SC, Park KK (December 2016). "The Pathogenetic Effect of Natural and Bacterial Toxins on Atopic Dermatitis". Toxins. 9 (1): 3. doi:10.3390/toxins9010003. PMC 5299398. PMID 28025545.
  2. ^ Irvine AD, McLean WH, Leung DY (October 2011). "Filaggrin mutations associated with skin and allergic diseases". The New England Journal of Medicine. 365 (14): 1315–27. doi:10.1056/nejmra1011040. PMID 21991953.
  3. ^ Egawa M, Nomura J, Iwaki H (May 2010). "The evaluation of the amount of cis- and trans-urocanic acid in the stratum corneum by Raman spectroscopy". Photochemical and Photobiological Sciences. 9 (5): 730–3. doi:10.1039/b9pp00143c. PMID 20442934.
  4. ^ Schwarz T (December 2005). "Mechanisms of UV-induced immunosuppression" (PDF). The Keio Journal of Medicine. 54 (4): 165–71. doi:10.2302/kjm.54.165. PMID 16452825.
  5. ^ Jungersted JM, Scheer H, Mempel M, Baurecht H, Cifuentes L, Høgh JK, Hellgren LI, Jemec GB, Agner T, Weidinger S (July 2010). "Stratum corneum lipids, skin barrier function and filaggrin mutations in patients with atopic eczema". Allergy. 65 (7): 911–8. doi:10.1111/j.1398-9995.2010.02326.x. PMID 20132155.
  6. ^ Fluhr JW, Elias PM, Man MQ, Hupe M, Selden C, Sundberg JP, Tschachler E, Eckhart L, Mauro TM, Feingold KR (August 2010). "Is the filaggrin-histidine-urocanic acid pathway essential for stratum corneum acidification?". The Journal of Investigative Dermatology. 130 (8): 2141–4. doi:10.1038/jid.2010.74. PMC 4548931. PMID 20376063.
  7. ^ a b Jaffe M (1874). "Ueber einen neuen Bestandtheil des Hundeharns" [Concerning a new constituent in the urine of dogs]. Berichte der Deutschen Chemischen Gesellschaft (in German). 7 (2): 1669–1673. doi:10.1002/cber.187400702225.
  8. ^ Jaffe M (1875). "Ueber die Urocaninsäure" [About urocanic acid]. Berichte der Deutschen Chemischen Gesellschaft (in German). 8 (1): 811–813. doi:10.1002/cber.187500801267.

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