Structure-Function Relationships in Mandelate Racemase and Muconate Lactonizing Enzyme

Abstract

Strains of Pseudomonads show considerable metabolic diversity by utilizing a large variety of organic compounds as sole carbon and energy sources. This metabolic diversity has both provided enzymologists with many new and unusual enzymes for mechanistic scrutiny and raised questions regarding the evolutionary pathways by which the metabolic diversity could have arisen. Our laboratories are interested in mechanistic, structural, and molecular biological aspects of the metabolism of mandelic acid by Pseudomonas putida. Both enantiomers of mandelic acid are oxidatively degraded to benzoic acid by the enzymes of the mandelate pathway (Figure 1), and benzoic acid, in turn, is oxidatively degraded to intermediates of the citric acid cycle by the enzymes of the β-ketoadipate pathway (Figure 2). In this chapter we summarize our recent observations on the mechanism of the reaction Open image in new window Figure 1 The mandelate pathway catalyzed by mandelate racemase and the structural and mechanistic relationship of this enzyme to muconate lactonizing enzyme, an enzyme central to the catabolism of benzoic acid and, therefore, mandelic acid. We have made the unexpected discovery that these enzymes are certainly divergently related and anticipate that molecular biological methods can be used to change muconate lactonizing enzyme into mandelate racemase and vice versa.