Histidine_ammonia-lyase

Histidine ammonia-lyase

Histidine ammonia-lyase

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Histidine ammonia-lyase (EC 4.3.1.3, histidase, histidinase) is an enzyme that in humans is encoded by the HAL gene.[5][6] It converts histidine into ammonia and urocanic acid. Its systematic name is L-histidine ammonia-lyase (urocanate-forming).

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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.[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]

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

Pathology

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

See also


References

  1. "Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
  2. "Mouse PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
  3. 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.
  4. 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

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


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