urocanase

Urocanase, also known as urocanate hydratase, is an enzyme involved in the catabolism of the amino acid histidine. It catalyzes the hydration of urocanic acid to 4-imidazolone-5-propionate, a reaction assigned EC 4.2.1.49. This step occurs in the histidine degradation pathway after histidine is converted to urocanate by histidine ammonia-lyase.

The product of the urocanase-catalyzed reaction, 4-imidazolone-5-propionate, is further processed by imidazolonepropionase to yield N-formiminoglutamate, which donates a formimino group to tetrahydrofolate and ultimately contributes to the generation of glutamate. Thus, urocanase links histidine breakdown to folate-dependent one-carbon metabolism.

Urocanase is found across a broad range of organisms, including bacteria, plants, and animals. In humans, the enzyme is encoded by the UROC1 gene. Rare inherited defects in urocanase can lead to urocanic aciduria, a metabolic condition characterized by elevated levels of urocanate in urine.

Clinical and research relevance centers on the enzyme’s role in histidine metabolism and its connection to folate-mediated one-carbon exchanges. Metabolic profiling of urocanate and related intermediates can be informative in certain diagnostic contexts, such as assessing folate status or diagnosing rare metabolic disorders.