Urocanic acid

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Urocanic acid
IUPAC name	3-(3H-imidazol-4-yl)prop-2-enoic acid
Identifiers
CAS number	[104-98-3]
PubChem	1178
MeSH	Urocanic+acid
SMILES	C1=C(NC=N1)C=CC(=O)O
Properties
Molecular formula	C6H6N2O2
Molar mass	138.124 g/mol
Melting point	225°C
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

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

Contents 1 Metabolism 2 Clinical significance 3 Function 4 History 5 See also 6 References 7 External links

[edit] 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.

[edit] Clinical significance

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

[edit] 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.

[edit] History

Urocanic acid was first isolated in 1874 by the chemist M. Jaffé from the urine of a dog,^[1] hence the name (Latin: urina = urine, and canis = dog).

[edit] See also

• Inborn error of metabolism

[edit] References

1. ^ Jaffé, M. (1874) Concerning a new constituent in the urine of dogs. Ber. Deut. Chem. Ges. 7, 1669-1673.

[edit] External links

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

v • d • e Amino acid metabolism metabolic intermediates K→acetyl-CoA lysine→ Saccharopine - Allysine - Alpha-aminoadipate - Alpha-ketoadipic acid - Glutaryl-CoA - Glutaconyl-CoA - Crotonyl-CoA - Beta-hydroxybutyryl-CoA leucine→ Alpha-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→glutamate histidine→ Urocanic acid - Imidazol-4-one-5-propionic acid - Formiminoglutamic acid - Glutamate-1-semialdehyde proline→ 1-Pyrroline-5-carboxylic acid arginine→ Ornithine - Putrescine - Agmatine G→propionyl-CoA methionine→ S-Adenosyl methionine - S-Adenosyl-L-homocysteine - Homocysteine - Cystathionine - alpha-Ketobutyric acid isoleucine→ 2,3-Dihydroxy-3-methylpentanoic acid - 2-Methylbutyryl-CoA - Tiglyl-CoA - 2-methylacetoacetyl-CoA valine→ Alpha-ketoisovalerate - Isobutyryl-CoA - Methacrylyl-CoA - 3-Hydroxyisobutyryl-CoA - 3-Hydroxyisobutyrate - 2-methyl-3-oxopropanoate threonine→ Alpha-ketobutyric acid propionyl-CoA→ Methylmalonyl-CoA G→fumarate phenylalanine→tyrosine→ 4-Hydroxyphenylpyruvic acid - Homogentisic acid - 4-Maleylacetoacetate Other cysteine+glutamate→glutathione gamma-Glutamylcysteine glycine→creatine Glycocyamine - Phosphocreatine - Creatinine Other Glycerate 3-phosphate (serine) - Cysteine sulfinic acid see also enzymes, disorders