Urocanase is the enzyme that catalyzes the second step in the degradation of histidine, the hydration of urocanate into imidazolonepropionate.

urocanate + H₂O 4,5-dihydro-4-oxo-5-imidazolepropanoate

Imidazol-4-one-5-propionic acid

Imidazol-4-one-5-propionic acid is an intermediate in the metabolism of histidine.-See also:* Urocanate hydratase* Urocanate* Formiminoglutamic acid...

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

Urocanic aciduria

Urocanic aciduria, also called urocanate hydratase deficiency or urocanase deficiency, is an autosomal recessive metabolic disorder caused by a deficiency of the enzyme urocanase. It is a secondary disorder of histidine metabolism.-Pathophysiology:...

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Urocanase is found in some bacteria (gene hutU), in the liver of many vertebrates and has also been found in the plant Trifolium repens (white clover). Urocanase is a protein of about 60 Kd, it binds tightly to NAD⁺ and uses it as an electrophil cofactor. A conserved cysteine has been found to be important for the catalytic mechanism and could be involved in the binding of the NAD⁺.