Urocanic acid

Urocanic acid
IUPAC name (E)-3-(1H-imidazol-4-yl)prop-2-enoic acid
Identifiers
CAS number	104-98-3
PubChem	1178
MeSH	Urocanic+acid
Jmol-3D images	Image 1
SMILES C1=C(NC=N1)C=CC(=O)O
Properties
Molecular formula	C6H6N2O2
Molar mass	138.124 g/mol
Melting point	225°C
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

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

Metabolism

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.

Function

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. The cis form is known to activate suppressor T cells.

History

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

See also

• Inborn error of metabolism

External links

• The Online Metabolic and Molecular Bases of Inherited Disease - Chapter 80 - An overview of disorders of histidine metabolism, including urocanic aciduria.