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1. 1.|Chorismate mutase-prephenate dehydrogenase from Escherichia coli K12 yielded only a single polypeptide species when electrophoresed under dissociating conditions. 2. 2.|The molecular weight of the dissociated enzyme was found to be about 40 000. 3. 3.|Maps of the dansylated tryptic peptides also indicated the presence of only a single polypeptide chain of about 40 000 molecular weight. 4. 4.|Evidence for homology between the enzymes from E. coli and Aerobacter aerogenes was obtained from comparison of maps of dansylated tryptic peptides.

1. Studies on the properties of dissociated chorismate mutase − prephenate dehydrogenase from Aerobacter aerogenes indicated the presence of subunits. Estimates of the molecular weight of the subunits following dissociation by sodium dodecyl sulphate or erea yielded a value of about 40000 which is half the molecular weight of the native enzyme. Two − dimentional chromatography of dansylated tryptic peptides from the protein also indicated that it consisted of two very similar or identical subunits of about 40000 molecular weight. The amino terminal end group of the protein was found to be methionine.

1. 1.|Chorismate mutase-prephenate dehydrogenase was purified to homogeneity from Escherichia coli K12. 2. 2.|Some of the general properties of the enzyme including preliminary kinetic data and sensitivity to inhibition by tyrosine have been determined. 3. 3.|The molecular weight of the native enzyme was found to be about 82 000. 4. 4.|The amino acid composition and preliminary data on the nature of the sulphydryl groups were also obtained. 5. 5.|The significance of the results in relation to those obtained previously for the enzyme from Aerobacter aerogenes is discussed.

The relationship between the sites for catalysis of two reactions by the bifunctional enzyme chorismate mutase--prephenate dehydrogenase has been investigated. The results are consistent with the occurrence of both reactions at one active site. Comparisons have been made between experimental data for the time course of the overall reaction and computer simulations, according to various models for the relationship between the mutase and dehydrogenase sites. A model based on a single active site is consistent with the time course data if a minor proportion of the chorismate that reacts can be converted through to (hydroxyphenyl)pyruvate without the intermediate release of prephenate. Consistent with this requirement, some channeling of radioactivity from chorismate to (hydroxyphenyl)pyruvate has been detected. A model based on two separate sites has also been considered; the simulations show that if this model applies there is no need to postulate any channeling of the intermediate, prephenate, between the sites and there must be marked inhibition of the dehydrogenase reaction by chorismate. Since channeling has been observed and chorismate increases the dehydrogenase rate under all conditions, the two-site model appears unlikely. Consistent with the one-site model are the observations that a variety of inactivating conditions cause parallel loss of mutase and dehydrogenase activity and that identical protection against inactivation of both mutase and dehydrogenase by iodoacetamide is afforded by prephenate.