Urocanic acid

Urocanic acid

Urocanic acid is an intermediate in the catabolism of histidine, an essential amino acid. It is found in the stratum corneum of the skin and plays a role in the skin's defense mechanism against ultraviolet (UV) radiation.

Structure and Properties

Urocanic acid is a crystalline compound with the chemical formula C6H6N2O2. It exists in two isomeric forms: trans-urocanic acid and cis-urocanic acid. The trans form is the predominant isomer in the skin, but upon exposure to UV radiation, it can isomerize to the cis form.

Biosynthesis

Urocanic acid is synthesized in the liver from histidine by the enzyme histidine ammonia-lyase (also known as histidase). This reaction is the first step in the degradation pathway of histidine.

Function in the Skin

In the skin, urocanic acid is a major component of the natural moisturizing factor (NMF). It absorbs UV radiation, thereby protecting deeper layers of the skin from damage. The conversion of trans-urocanic acid to cis-urocanic acid upon UV exposure is thought to play a role in the immune response of the skin.

Clinical Significance

Abnormal levels of urocanic acid in the skin can be associated with certain skin disorders. For example, decreased levels of urocanic acid have been observed in patients with atopic dermatitis. Additionally, urocanic acid has been studied for its potential role in photocarcinogenesis and photoimmunosuppression.

Related Pages

• Histidine
• Stratum corneum
• Natural moisturizing factor
• Histidine ammonia-lyase
• Atopic dermatitis
• Photocarcinogenesis
• Photoimmunosuppression

See Also

• Amino acid metabolism
• Skin physiology
• Ultraviolet radiation