EC - 2-hydroxymuconate tautomerase

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IntEnz Enzyme Nomenclature


Accepted name:
2-hydroxymuconate tautomerase
Other names:
4-oxalocrotonate tautomerase [misleading]
4-oxalocrotonate isomerase [misleading]
cnbG (gene name)
praC (gene name)
xylH (gene name)
Systematic name:
(2Z,4E)-2-hydroxyhexa-2,4-dienedioate keto--enol isomerase



Involved in the meta-cleavage pathway for the degradation of phenols, modified phenols and catechols. The enol form (2Z,4E)-2-hydroxyhexa-2,4-dienedioate is produced as part of this pathway and is converted to the keto form (3E)-2-oxohex-3-enedioate by the enzyme [6]. Another keto form, (4E)-2-oxohex-4-enedioate (4-oxalocrotonate), was originally thought to be produced by the enzyme [1,2] but later shown to be produced non-enzymatically [5].

Links to other databases

Enzymes and pathways: NC-IUBMB , BRENDA , DIAGRAM , ExplorEnz , ENZYME@ExPASy , KEGG , MetaCyc , UniPathway
Structural data: CSA , EC2PDB


  1. Whitman, C.P., Aird, B.A., Gillespie, W.R. and Stolowich, N.J.
    Chemical and enzymatic ketonization of 2-hydroxymuconate, a conjugated enol.
    J. Am. Chem. Soc. 113 : 3154-3162 (1991).
  2. Whitman, C.P., Hajipour, G., Watson, R.J., Johnson, W.H., Jr., Bembenek, M.E. and Stolowich, N.J.
    Stereospecific ketonization of 2-hydroxymuconate by 4-oxalocrotonate tautomerase and 5-(carboxymethyl)-2-hydroxymuconate isomerase.
    J. Am. Chem. Soc. 114 : 10104-10110 (1992).
  3. Subramanya, H. S., Roper, D. I., Dauter, Z., Dodson, E. J., Davies, G. J., Wilson, K. S., Wigley, D. B.
    Enzymatic ketonization of 2-hydroxymuconate: specificity and mechanism investigated by the crystal structures of two isomerases.
    Biochemistry 35 : 792-802 (1996). [PMID: 8547259]
  4. Stivers, J. T., Abeygunawardana, C., Mildvan, A. S., Hajipour, G., Whitman, C. P., Chen, L. H.
    Catalytic role of the amino-terminal proline in 4-oxalocrotonate tautomerase: affinity labeling and heteronuclear NMR studies.
    Biochemistry 35 : 803-813 (1996). [PMID: 8547260]
  5. Wang, S. C., Johnson, W. H., Czerwinski, R. M., Stamps, S. L., Whitman, C. P.
    Kinetic and stereochemical analysis of YwhB, a 4-oxalocrotonate tautomerase homologue in Bacillus subtilis: mechanistic implications for the YwhB- and 4-oxalocrotonate tautomerase-catalyzed reactions.
    Biochemistry 46 : 11919-11929 (2007). [PMID: 17902707]
  6. Kasai, D., Fujinami, T., Abe, T., Mase, K., Katayama, Y., Fukuda, M., Masai, E.
    Uncovering the protocatechuate 2,3-cleavage pathway genes.
    J. Bacteriol. 191 : 6758-6768 (2009). [PMID: 19717587]

[EC created 2012]