Regulation of the Enzymes of the β‐Ketoadipate Pathway in Moraxella calcoacetica

The inducible enzymes responsible for the dissimilation of aromatic compounds through the β‐ketoadipate pathway by Moraxella calcoacetica are subject to a high degree of coordinate control. The five enzymes which catalyze the conversion of protocatechuate to β‐ketoadipyl‐CoA are coordinately synthesized, the probable inducer being protocatechuate. In the conversion of catechol to β‐ketoadipyl‐CoA, there are two separate inductive events, though both are mediated by one metabolite‐inducer, cis,cis ‐muconate. One is the induction of catechol oxygenase; the other is the coordinate induction of the four enzymes that catalyze conversion of cic,cis ‐muconate to β‐ketoadipyl‐CoA. Although the catechol and protocatechuate branches of the β‐ketoadipate pathway converge metabolically with the formation of β‐ketoadipate enol‐lactone, the two step‐reactions required for the conversion of this intermediate to β‐ketoadipyl‐CoA are mediated by two isofunctional sets of inducible enzymes, one controlled coordinately with enzymes mediating steps specific to the catechol branch, the other coordinately with enzymes mediating steps specific to the protocatechuate branch. The differing control mechanisms which govern synthesis of the enzymes of the β‐ketoadipate pathway in Moraxella calcoacetica and in Pseudomonas putida are compared and discussed.