Urocanase (also known as imidazolonepropionate hydrolase or urocanate hydratase) is an enzyme (EC 4.2.1.49) that in humans is encoded by the geneUROC1. This enzyme catalyzes the second step in the degradation of histidine, the hydration of urocanic acid to imidazol-4-one-5-propionic acid.
The protein itself is composed of 676 amino acids which then fold, producing the final product which has two identical subunits, making the enzyme a homodimer.
To catalyze the hydrolysis of urocanate in the catabolic pathway of L-histidine the enzyme utilizes its two nicotinamide adenine dinucleotide (NAD+) groups. These act as electrophiles, attaching to the top carbon of the urocanate which leads to sigmatropic rearrangement of the urocanate molecule. This rearrangement allows for the addition of a water molecule, converting the urocanic acid into imidazol-4-one-5-propionic acid.
Inherited deficiency of urocanase leads to elevated levels of urocanic acid in the urine, a condition known as urocanic aciduria.
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+.
↑"Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
↑"Mouse PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
↑Rétey J (October 1994). "The urocanase story: a novel role of NAD+ as electrophile". Archives of Biochemistry and Biophysics. 314 (1): 1–16. doi:10.1006/abbi.1994.1405. PMID7944380.
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