Overlapping evolutionary affinities revealed by comparison of amino acid compositions

Comparison of the amino acid compositions of purified proteins indicates the presence of overlapping evolutionary affinities among enzymes of the beta-ketoadipate pathway. Isofunctional enzymes from different bacterial genera share a common evolutionary origin. Moreover, enzymes that mediate isofunctional or chemically analogous reactions within an organism appear to be evolutionarily homologous. Most remarkably, closely similar amino acid compositions are found in enzymes that mediate the following consecutive metabolic steps: lactonization, decarboxylation, hydrolysis, and transfer of a thioester bond.