Urocanic acid
pair of isomers
Urocanic acid (formally trans-Urocanic acid) is an intermediate in the catabolism of L-histidine. The cis-urocanic acid isomer is rare.
Ultraviolet radiation absorption
Urocanic acid is a chromophore with a strong, broad, and largely structureless absorption band that spans the UV-C and UV-B regions of the electromagnetic spectrum. Experimental measurements consistently find the absorption maximum, λmax, in the range of 267 nm to 280 nm, with the precise value being sensitive to its solvent's pH and polarity.
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.
An important role for the onset of atopic dermatitis and asthma has been attributed to filaggrin, a skin precursor of urocanic acid.
Urocanic acid is thought to be a significant attractant of the nematode parasite Strongyloides stercoralis, in part because of relatively high levels in the plantar surfaces of the feet, the site through which this parasite often enters the body.
Function
Urocanic acid is found in animal sweat and skin.
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