Urocanic acid

Urocanic acid
Names

IUPAC name (E)-3-(1H-imidazol-4-yl)prop-2-enoic acid
Identifiers
CAS Number	104-98-3^Y
ChEBI	CHEBI:30817^N
ChemSpider	643824^N
Jmol interactive 3D	Image
MeSH	Urocanic+acid
PubChem	1178
InChI InChI=1S/C6H6N2O2/c9-6(10)2-1-5-3-7-4-8-5/h1-4H,(H,7,8)(H,9,10)/b2-1+^N Key: LOIYMIARKYCTBW-OWOJBTEDSA-N^N InChI=1/C6H6N2O2/c9-6(10)2-1-5-3-7-4-8-5/h1-4H,(H,7,8)(H,9,10)/b2-1+ Key: LOIYMIARKYCTBW-OWOJBTEDBA
SMILES c1c(nc[nH]1)/C=C/C(=O)O
Properties
Chemical formula	C₆H₆N₂O₂
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).
N verify (what is ^YN ?)
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.^[1] The cis form is known to activate regulatory T cells.^[2]

History

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).

References

↑ 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.
↑ Schwarz T: Mechanisms of UV-induced immunosuppression. Keio J Med 2005;54(4):165-171.
↑ Jaffé, M. (1874). "Concerning a new constituent in the urine of dogs". Ber. Deut. Chem. Ges. 7: 1669–1673.
↑ M. Jaffe: Ueber die Urocaninsäure. In: Berichte der deutschen chemischen Gesellschaft. - Weinheim : Wiley-VCH, ISSN 0365-9496 Vol. 8 (1. 1875), p. 811-813.
↑ 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.

External links

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

Amino acid metabolism metabolic intermediates

K→acetyl-CoA

lysine→	Saccharopine Allysine α-Aminoadipic acid α-Ketoadipate Glutaryl-CoA Glutaconyl-CoA Crotonyl-CoA β-Hydroxybutyryl-CoA

leucine→	α-Ketoisocaproic acid Isovaleryl-CoA 3-Methylcrotonyl-CoA 3-Methylglutaconyl-CoA HMG-CoA

tryptophan→alanine→	N'-Formylkynurenine Kynurenine Anthranilic acid 3-Hydroxykynurenine 3-Hydroxyanthranilic acid 2-Amino-3-carboxymuconic semialdehyde 2-Aminomuconic semialdehyde 2-Aminomuconic acid Glutaryl-CoA

G→pyruvate→citrate

glycine→serine→	3-Phosphoglyceric acid glycine→creatine: Glycocyamine Phosphocreatine Creatinine

G→glutamate→
α-ketoglutarate

histidine→	Urocanic acid Imidazol-4-one-5-propionic acid Formiminoglutamic acid Glutamate-1-semialdehyde

proline→	1-Pyrroline-5-carboxylic acid

arginine→	Agmatine Ornithine Cadaverine Putrescine

other	cysteine+glutamate→glutathione: γ-Glutamylcysteine

G→propionyl-CoA→
succinyl-CoA

valine→	α-Ketoisovaleric acid Isobutyryl-CoA Methacrylyl-CoA 3-Hydroxyisobutyryl-CoA 3-Hydroxyisobutyric acid 2-Methyl-3-oxopropanoic acid

isoleucine→	2,3-Dihydroxy-3-methylpentanoic acid 2-Methylbutyryl-CoA Tiglyl-CoA 2-Methylacetoacetyl-CoA

methionine→	generation of homocysteine: S-Adenosyl methionine S-Adenosyl-L-homocysteine Homocysteine conversion to cysteine: Cystathionine alpha-Ketobutyric acid+Cysteine

threonine→	α-Ketobutyric acid

propionyl-CoA→	Methylmalonyl-CoA

G→fumarate

phenylalanine→tyrosine→	4-Hydroxyphenylpyruvic acid Homogentisic acid 4-Maleylacetoacetic acid

G→oxaloacetate

see urea cycle

Other

Cysteine metabolism	Cysteine sulfinic acid

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