IUBMB Enzyme Nomenclature


Accepted name: 2-hydroxymuconate tautomerase

Reaction: (2Z,4E)-2-hydroxyhexa-2,4-dienedioate = (3E)-2-oxohex-3-enedioate

Glossary: (2Z,4E)-2-hydroxyhexa-2,4-dienedioate = (2Z,4E)-2-hydroxymuconate

For diagram of reaction click here.

Other name(s): 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 ketoenol isomerase

Comments: 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: BRENDA, EXPASY, KEGG, Metacyc, CAS registry number:


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 (1991) 3154-3162.

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 (1992) 10104-10110.

3. Subramanya, H.S., Roper, D.I., Dauter, Z., Dodson, E.J., Davies, G.J., Wilson, K.S. and Wigley, D.B. Enzymatic ketonization of 2-hydroxymuconate: specificity and mechanism investigated by the crystal structures of two isomerases. Biochemistry 35 (1996) 792-802. [PMID: 8547259]

4. Stivers, J.T., Abeygunawardana, C., Mildvan, A.S., Hajipour, G., Whitman, C.P. and Chen, L.H. Catalytic role of the amino-terminal proline in 4-oxalocrotonate tautomerase: affinity labeling and heteronuclear NMR studies. Biochemistry 35 (1996) 803-813. [PMID: 8547260]

5. Wang, S.C., Johnson, W.H., Jr., Czerwinski, R.M., Stamps, S.L. and 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 (2007) 11919-11929. [PMID: 17902707]

6. Kasai, D., Fujinami, T., Abe, T., Mase, K., Katayama, Y., Fukuda, M. and Masai, E. Uncovering the protocatechuate 2,3-cleavage pathway genes. J. Bacteriol. 191 (2009) 6758-6768. [PMID: 19717587]

[EC created 2012]

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