Kinetic studies on the reactions catalyzed by chorismate mutase-prephenate dehydrogenase from Aerobacter aerogenes

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Abstract
Steady-state kinetic techniques were used to investigate each of the reactions catalyzed by the bifunctional enzyme, chorismate mutase[EC 5.4.99.5]-prephenate dehydrogenase [EC 4.2.1.51], from A. aerogenes. The results of steady-state velocity studies in the absence of products, and product and dead-end inhibition studies, suggest that the prephenate dehydrogenase reaction conforms to a rapid equilibrium random mechanism which involves the formation of 2 dead-end complexes, namely, enzyme-NADH-prephenate and enzyme-NAD+-hydroxyphenylpyruvate. Chorismate functions as an activator of the dehydrogenase while both prephenate and hydroxyphenylpyruvate acted as competitive inhibitors in the mutase reaction. NAD+ and NADH function as activators of the mutase. Values of the kinetic parameters associated with the mutase and dehydrogenase reactions were determined and the results discussed in terms of possible relationships between the catalytic sites for the 2 reactions. The data appear to be consistent with the enzyme having either a single site at which both reactions occur or 2 separate sites which possess similar kinetic properties.
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