Chorismate Mutase-Prephenate Dehydratase from Escherichia coli K-12

Abstract

Abstract The results of kinetic investigations with pure chorismate mutase-prephenate dehydratase from Escherichia coli K-12 were as follows: a pH optimum of 7.3 for the mutase activity, a Km of 0.045 mm for chorismate, and a Km of 1.0 mm for prephenate. l-Phenylalanine inhibited both the mutase and the dehydratase activities. In each case the relationship between activity and concentration of l-phenylalanine was sigmoidal and analysis of the results by the Hill equation gave values of n' = 2.3. d-Phenylalanine and l-tryptophan did not inhibit either activity whilst varying degrees of inhibition were observed with o-, m-, and p-monosubstituted fluoro-, chloro-, and hydroxyphenylalanines. Investigations with other phenylalanine analogues indicated that the α-NH2 group is not essential for inhibition, although it is required for maximal effect. There is an absolute requirement for an unmodified α-COOH group. Thiol compounds such as β-mercaptoethanol and dithioerythritol have little effect on the mutase activity but stimulate the dehydratase activity by approximately 150%.