The Conversion of Catechol and Protocatechuate to β-Ketoadipate by Pseudomonas putida

Abstract

Two new intermediates were identified in the protocatechuate pathway of Pseudomonas putida. The first of these, γ-carboxymuconolactone (γ-carboxy-γ-carboxymethyl-Δα-butenolide), is the product of the enzymic lactonization of β-carboxy-cis, cis-muconate. Enzymic decarboxylation of γ-carboxymuconolactone gives rise to β-ketoadipate enollactone (γ-carboxymethyl-Δβ-butenolide), the second newly discovered intermediate in the protocatechuate pathway. β-Ketoadipate enol-lactone, which was isolated and physically characterized, is also an intermediate in the catechol pathway; the catechol and protocatechuate pathways converge at this point. β-Ketoadipate enol-lactone is hydrolyzed to β-ketoadipate by an enzyme which is essential for utilization of either catechol or protocatechuate. Studies with Moraxella lwoffii showed that this organism also degrades protocatechuate and catechol by the pathways characteristic of P. putida. Elucidation of the bacterial pathway for the dissimilation of protocatechuate revealed that the three step-reactions responsible for the conversion of this compound to β-ketoadipate enol-lactone are analogous with the step-reactions responsible for the conversion of catechol to β-ketoadipate enol-lactone.