Regulation of the enzymes of the beta-ketoadipate pathway in Moraxella calcoacetica. 4. Constitutive synthesis of beta-ketoadipate succinyl-CoA transferases II and 3.

Abstract

Mutants of Moraxella calcoacetica which synthesize constitutively β‐ketoadipate succinyl‐CoA transferase, but in which all other enzymes of the β‐ketoadipate pathway are still normally inducible, have been isolated by selection for the ability to grow with β‐ketoadipate. The constitutively synthesized transferase was identified as transferase III. This enzyme is induced in the wild type by adipate and its physiological function is probably adipate activation. The properties of these constitutive mutants confirm that the synthesis of transferase III is regulated independently of the synthesis of enzymes that mediate reactions of the β‐ketoadipate pathway.Two phenotypically different classes of mutants which synthesize transferase II constitutively have also been isolated by the same selective procedure. Both classes of mutants synthesize constitutively the five enzymes that convert catechol to β‐ketoadipyl‐CoA. Strict coordinacy between four of these enzymes (muconate lactonizing enzyme, muconolactone isomerase, β‐ketoadipate enol‐lactone hydrolase II and β‐ketoadipate succinyl‐CoA transferase II) is maintained in one class of mutants. However in the other class this coordinacy is destroyed and muconate lactonizing enzyme is synthesized in succinate‐grown cells at a relative level much lower than those of the other three enzymes. These findings are discussed and evaluated in terms of earlier evidence concerning the regulation of the synthesis of enzymes of the catechol branch by M. calcoacetica.