Histidine ammonia-lyase (EC4.3.1.3, histidase, histidinase) is an enzyme that in humans is encoded by the HALgene.[5][6] It converts histidine into ammonia and urocanic acid. Its systematic name is L-histidine ammonia-lyase (urocanate-forming).
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.
^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. PMID8530107.
^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. PMID10220322.
Suchi M, Harada N, Wada Y, Takagi Y (1993). "Molecular cloning of a cDNA encoding human histidase". Biochim. Biophys. Acta. 1216 (2): 293–5. doi:10.1016/0167-4781(93)90157-9. PMID7916645.
Davila S, Froeling FE, Tan A, et al. (2010). "New genetic associations detected in a host response study to hepatitis B vaccine". Genes Immun. 11 (3): 232–8. doi:10.1038/gene.2010.1. PMID20237496. S2CID11183658.
Eckhart L, Schmidt M, Mildner M, et al. (2008). "Histidase expression in human epidermal keratinocytes: regulation by differentiation status and all-trans retinoic acid". J. Dermatol. Sci. 50 (3): 209–15. doi:10.1016/j.jdermsci.2007.12.009. PMID18280705.
Kawai Y, Moriyama A, Asai K, et al. (2005). "Molecular characterization of histidinemia: identification of four missense mutations in the histidase gene". Hum. Genet. 116 (5): 340–6. doi:10.1007/s00439-004-1232-5. PMID15806399. S2CID33960184.
Taylor RG, García-Heras J, Sadler SJ, et al. (1991). "Localization of histidase to human chromosome region 12q22→q24.1 and mouse chromosome region 10C2→D1". Cytogenet. Cell Genet. 56 (3–4): 178–81. doi:10.1159/000133082. PMID2055114.
Alemán G, Ortíz V, Langley E, et al. (2005). "Regulation by glucagon of the rat histidase gene promoter in cultured rat hepatocytes and human hepatoblastoma cells". Am. J. Physiol. Endocrinol. Metab. 289 (1): E172–9. doi:10.1152/ajpendo.00584.2004. PMID15741241.
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