Beta-ketoadipate enol-lactone hydrolases I and II from Acinetobacter calcoaceticus

Beta-Ketoadipate enol-lactone hydrolase catalyzes a common step in the utilization of protocatechuate and cis,cis-muconate by bacteria. Either of the two compounds elicits the synthesize of an enol-lactone hydrolase in Acinetobacter. The enol-lactone hydrolase that is induced by each compound was purified, and the properties of the proteins were compared. Both enzymes appear to be dimers with molecular weights of approximately 25,000. The amino acid compositions of the enzymes differ, and the two proteins do not cross-react serologically. The NH2-terminal amino acid residue of the protocatechuate-induced enol-lactone hydrolase (ELH I) is methionine and the NH2-terminal amino acid residue of the cis,cis-muconate-induced enol-lactone hydrolase (ELH II) is proline. Therefore, ELH I and ELH II appear to be the products of different structural genes. The serological specificity of ELH I and ELH II made it possible to demonstrate the mutually independent regulation of their synthesis in wild type cells and in constitutive mutant strains. The synthesis of ELH I is not impaired in mutant strains that cannot synthesize ELH II. The rapid characterization of mutant strains that produce ELH I or ELH II constitutively was made possible by the development of pH indicator enzyme assays that were performed with toluenized cells. cis,trans-Muconate, which does not support the growth of Acinetobacter, elicits the synthesis of the enzymes that normally are induced by cis,cis-muconate to 20% of fully induced levels.