Comparison of the two isofunctional enol-lactone hydrolases from Acinetobacter calcoaceticus

The rates of thermal denaturation and the molecular weights of the two isofunctional enol-lactone hydrolases (ELH I and ELH II) of Acinetobacter calcoaceticus were determined. The molecular weights of ELH I and ELH II were found by gel filtration to be approximately 24,000 and 21,000, respectively. In crude extract at 45 C the two enzymes showed a marked difference in rate of thermal denaturation. After chromatography on Sephadex G-100, however, the rates were nearly identical. The thermolability of ELH II in crude extract was shown to be due to its sensitivity to an unidentified component of the crude extract which modified its rate of thermal denaturation. In the light of the physical similarities of the two enzymes, it is concluded that the different regulatory patterns imposed upon the two enzymes do not provide sufficient evidence that they are the product of two different structural genes.