Identification and Purification of Distinct Isomerase and Decarboxylase Enzymes Involved in the 4‐Hydroxyphenylacetate Catabolic Pathway of Escherichia coli

The possible involvement of an isomerase in the 4‐hydroxyphenylacetate meta ‐cleavage pathway has been studied. 5‐Carboxymethyl‐2‐hydroxymuconate has been shown to undergo both spontaneous and enzymecatalysed isomerisation to give 5‐carboxymethyl‐2‐oxo‐hex‐3‐ene‐1,6‐dioate, a compound with an absorbance maximum at 246 nm. The latter compound rather than the former is the substrate for a decarboxylase that produces 2‐hydroxyhepta‐2,4‐diene‐1,7‐dioate. The isomerase and decarboxylase enzymes have been purified to over 90% homogeneity. Mg 2+ is required for the decarboxylase reaction but not for the isomerase.