Health Dictionary Find a Doctor

Histidine ammonia-lyase

Histidine ammonia-lyase (or histidase, or histidinase) is an enzyme that in humans is encoded by the HAL gene.[1][2] Histidase converts histidine into ammonia and urocanic acid.

Function

Function

Histidine ammonia-lyase is a cytosolic enzyme catalyzing the first reaction in histidine catabolism, the nonoxidative deamination of L-histidine to trans-urocanic acid.[1] The reaction is catalyzed by 3,5-dihydro-5-methyldiene-4H-imidazol-4-one, an electrophilic co-factor which is formed autocatalytically by cyclization of the protein backbone of the enzyme.[3]

Pathology

Pathology

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

References

References

  1. 1.0 1.1 “Entrez Gene: histidine ammonia-lyase”.
  2. Suchi M, Sano H, Mizuno H, Wada Y (September 1995). “Molecular cloning and structural characterization of the human histidase gene (HAL)”. Genomics. 29 (1): 98–104. doi:10.1006/geno.1995.1219. PMID 8530107.
  3. Schwede, TF; Rétey, J; Schulz, GE (Apr 27, 1999). “Crystal structure of histidine ammonia-lyase revealing a novel polypeptide modification as the catalytic electrophile”. Biochemistry. 38 (17): 5355–5361. doi:10.1021/bi982929q. PMID 10220322.
Further reading

Further reading

External links

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


Looking for the patient version?

Back to the patient-friendly article

© 2026 MyEClinic – IFTM Institut für Telematik in der Medizin GmbH