Urocanic acid

Urocanic acid
Preferred IUPAC name
(2E)-3-(1H-imidazol-4-yl)prop-2-enoic acid
Other names
(E)-3-(1H-imidazol-4-yl)acrylic acid
104-98-3 YesY
3D model (Jmol) Interactive image
ChemSpider 643824 N
ECHA InfoCard 100.002.963
MeSH Urocanic+acid
PubChem 1178
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

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


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.[1] The cis form is known to activate regulatory T cells.[2]


Urocanic acid was first isolated in 1874 by the chemist Max Jaffé from the urine of a dog,[3][4][5] hence the name (Latin: urina = urine, and canis = dog).

See also


  1. Egawa M, Nomura J, Iwaki H: The evaluation of the amount of cis- and trans-urocanic acid in the stratum corneum by Raman spectroscopy. Photochem. Photobiol. Sci., 2010, 9, 730-733.
  2. Schwarz T: Mechanisms of UV-induced immunosuppression. Keio J Med 2005;54(4):165-171.
  3. Jaffé, M. (1874). "Concerning a new constituent in the urine of dogs". Ber. Deut. Chem. Ges. 7: 1669–1673.
  4. M. Jaffe: Ueber die Urocaninsäure. In: Berichte der deutschen chemischen Gesellschaft. - Weinheim : Wiley-VCH, ISSN 0365-9496 Vol. 8 (1. 1875), p. 811-813.
  5. M. Jaffe: Ueber einen neuen Bestandtheil des Hundeharns. In: Berichte der deutschen chemischen Gesellschaft. - Weinheim : Wiley-VCH, ISSN 0365-9496 Vol. 7 (2. 1874), p. 1669-1673.
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