Evolutionarily homologous alpha 2 beta 2 oligomeric structures in beta-ketoadipate succinyl-CoA transferases from...

Homogeneous beta-ketoadipate succinyl-CoA transferase (EC 2.8.3.6) preparations were obtained from extracts of Acinetobacter calcoaceticus and Pseudomonas putida. Gel filtration indicated that the respective transferases have similar molecular weights of 108,000 and 109,000; each transferase appears to have an alpha 2 beta 2 oligomeric structure formed by association of nonidentical subunits with a molecular weight of about 25,000. The subunits were separated by sodium dodecyl sulfate-gel electrophoresis, and differences in their primary structures were revealed by determination of the NH2-terminal amino acid sequences of the oligomers. The transferases cross-react immunologically and possess similar amino acid compositions. These are remarkably similar to the amino acid compositions of gamma-carboxymuconolactone decarboxylases (EC 4.1.1.44) and beta-ketoadipate enol-lactone hydrolases (EC 3.1.1.24), enzymes that mediate consecutive reactions preceding the transferase step in the beta-ketoadipate pathway.