Metabolism of 4-chloro-2-methylphenoxyacetate by a soil pseudomonad. Ring-fission, lactonizing and delactonizing enzymes

1. A cell-free system, prepared from Pseudomonas N.C.I.B. 9340 grown on 4-chloro-2-methylphenoxyacetate (MCPA) was shown to catalyse the reaction sequence: 5-chloro-3-methylcatechol --> cis-cis-gamma-chloro-alpha-methylmuconate --> gamma-carboxymethylene-alpha-methyl-Delta(alphabeta)-butenolide --> gamma-hydroxy-alpha-methylmuconate. 2. The activity of the three enzymes involved in these reactions was completely resolved and the lactonizing and delactonizing enzymes were separated. 3. This part of the metabolic pathway of 4-chloro-2-methylphenoxyacetate is thus confirmed for this bacterium. 4. The ring-fission oxygenase required Fe(2+) or Fe(3+) and reduced glutathione for activity; the lactonizing enzyme is stimulated by Mn(2+), Mg(2+), Co(2+) and Fe(2+); no cofactor requirement could be demonstrated for the delactonizing enzyme. 5. cis-cis-gamma-Chloro-alpha-methylmuconic acid was isolated and found to be somewhat unstable, readily lactonizing to gamma-carboxymethylene-alpha-methyl-Delta(alphabeta)-butenolide. 6. Enzymically the lactonization appears to be a single-step dehydrochlorinase reaction.