Histidine ammonia-lyase

Histidine ammonia-lyase (or histidase, or histidinase) is an is_associated_with::enzyme that in humans is encoded by the HAL is_associated_with::gene. Histidase converts is_associated_with::histidine into is_associated_with::ammonia and is_associated_with::urocanic acid.

Function
Histidine ammonia-lyase is a cytosolic enzyme catalyzing the first reaction in histidine catabolism, the nonoxidative is_associated_with::deamination of L-histidine to trans-urocanic acid. The reaction is catalyzed by an electrophilic co-factor which is formed autocatalytically by cyclization of the protein backbone of the enzyme.

Pathology
Mutations in the gene for histidase are associated with is_associated_with::histidinemia and is_associated_with::urocanic aciduria.