IUBMB Enzyme Nomenclature


Accepted name: histidine ammonia-lyase

Reaction: L-histidine = urocanate + NH3

For diagram of reaction click here

Glossary: urocanate = (E)-3-(imidazol-4-yl)propenoate

Other name(s): histidase; histidinase; histidine α-deaminase; L-histidine ammonia-lyase

Systematic name: L-histidine ammonia-lyase (urocanate-forming)

Comments: This enzyme is a member of the aromatic amino acid lyase family, other members of which are EC (tyrosine ammonia-lyase), EC (phenylalanine ammonia-lyase) and EC (phenylalanine/tyrosine ammonia-lyase). The enzyme contains the cofactor 3,5-dihydro-5-methylidene-4H-imidazol-4-one (MIO), which is common to this family [4]. This unique cofactor is formed autocatalytically by cyclization and dehydration of the three amino-acid residues alanine, serine and glycine [5]. This enzyme catalyses the first step in the degradation of histidine and the product, urocanic acid, is further metabolized to glutamate [2,3].

Links to other databases: BRENDA, EXPASY, GTD, KEGG, Metacyc, PDB, CAS registry number: 9013-75-6


1. Mehler, A.H. and Tabor, H. Deamination of histidine to form urocanic acid in liver. J. Biol. Chem. 201 (1953) 775-784. [PMID: 13061415]

2. Watts, K.T., Mijts, B.N., Lee, P.C., Manning, A.J. and Schmidt-Dannert, C. Discovery of a substrate selectivity switch in tyrosine ammonia-lyase, a member of the aromatic amino acid lyase family. Chem. Biol. 13 (2006) 1317-1326. [PMID: 17185227]

3. Poppe, L. and Rétey, J. Friedel-Crafts-type mechanism for the enzymatic elimination of ammonia from histidine and phenylalanine. Angew. Chem. Int. Ed. Engl. 44 (2005) 3668-3688. [PMID: 15906398]

4. Louie, G.V., Bowman, M.E., Moffitt, M.C., Baiga, T.J., Moore, B.S. and Noel, J.P. Structural determinants and modulation of substrate specificity in phenylalanine-tyrosine ammonia-lyases. Chem. Biol. 13 (2006) 1327-1338. [PMID: 17185228]

5. Schwede, T.F., Rétey, J. and Schulz, G.E. Crystal structure of histidine ammonia-lyase revealing a novel polypeptide modification as the catalytic electrophile. Biochemistry 38 (1999) 5355-5361. [PMID: 10220322]

[EC created 1961, modified 2008]

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