Involved in the meta-cleavage pathway for the degradation of phenols, modified phenols and catechols. The enzyme has been reported to accept multiple tautomeric forms [1-4]. However, careful analysis of the stability of the different tautomers, as well as characterization of the enzyme that produces its substrate, EC?5.3.2.6, 2-hydroxymuconate tautomerase, showed that the actual substrate for the enzyme is (3E)-2-oxohex-3-enedioate [4].