Histidine ammonia-lyase

303415109ENSG00000084110ENSMUSG00000020017P42357P35492NM_001258333NM_001258334NM_002108NM_010401NP_001245262NP_001245263NP_002099NP_034531Histidine ammonia-lyase (EC 4.3.1.3, histidase, histidinase) is an enzyme that in humans is encoded by the HAL gene.

Histidine ammonia-lyase is a cytosolic enzyme catalyzing the first reaction in histidine catabolism, the nonoxidative deamination of L-histidine to trans-urocanic acid.

[5] The reaction is catalyzed by 3,5-dihydro-5-methyldiene-4H-imidazol-4-one (MIO), an electrophilic cofactor which is formed autocatalytically by cyclization of the protein backbone of the enzyme.

[7]Mutations in the gene for histidase are associated with histidinemia and urocanic aciduria.

This article incorporates text from the United States National Library of Medicine, which is in the public domain.

Proposed autocatalytic formation of MIO cofactor in another enzyme, phenylalanine ammonia-lyase , from the tripeptide Ala-Ser-Gly by two water elimination steps.