is an intermediate in the catabolism
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.
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. The cis form is known to activate suppressor T cells
Urocanic acid was first isolated in 1874 by the chemist M. Jaffé from the urine of a dog, hence the name (Latin
= urine, and canis