Characterization of Monofunctional Chorismate Mutase/Prephenate Dehydrogenase Enzymes Obtained via Mutagenesis of Recombinant Plasmids in vitro

Mutagenesis in vitro has been used to obtain mutant forms of the bifunctional enzyme, chorismate mutase/prephenate dehydrogenase. Plasmid DNA containing the genes that code for the enzyme was treated with hydroxylamine and the resulting products were used to transform strains of Escherichia coli. Two types of mutant were isolated. One contained enzyme which was mutase-positive, dehydrogenase-negative while the other did not exhibit either activity. Kinetic and physical analysis of one of the purified monofunctional enzymes showed that the loss of dehydrogenase activity was due to modification of the binding site for NAD. The results open the way for molecular studies of structure-function relationships with this bifunctional enzyme.