Chorismate mutase-prephenate dehydrogenase from Escherichia coli kinetic mechanism of the prephenate dehydrogenase reaction

Abstract

The mechanism of the dehydrogenase reaction catalyzed by chorismate mutase-prephenate dehydrogenase (chorismate pyruvatemutase, EC 5.4.99.5-prephenate: NAD + oxidoreductase (decarboxylating), EC 1.3.1.12) has been investigated using steady-state kinetic techniques. The steady-state velocity pattern in the absence of products as well as product and dead-end inhibition patterns are consistent with a random mechanism in which two dead-end complexes, E-NADH-prephenate and E-NAD-hydroxyphenylpyruvate, are formed, and in which all steps are in rapid equilibrium except that concerned with the interconversion of central ternary complexes. Values have been determined for the maximum velocity of the reaction as well as for the kinetic parameters associated with the combination of substrates, products and the dead-end inhibitor, AMP, with various enzyme forms. The results indicate that when albumin is present in the reaction mixture, the presence of one substrate on the enzyme does not affect the combination of the second substrate. On the other hand, the binding of 4-hydroxyphenylpyruvate is enhanced by the presence of NAD and the binding of NADH is enhanced by the presence of prephenate on the enzyme. These results contrast with the finding that the inhibitory analogue, AMP, binds more strongly to the free enzyme than to the E-prephenate complex.