Purification and Properties of 3-Deoxy- d -Arabinoheptulosonic Acid-7-Phosphate Synthetase (phe) from a λ aroG + Transductant of Escherichia coli

By incorporating aroG, the structural gene for 3-deoxy-d-arabinoheptulosonic acid-7-phosphate (DAHP) synthetase (phe), into the genome of a heat-inducible susR60 mutant of phage lambda, it has been possible to increase the intracellular levels of DAHP synthetase (phe) in a lysogenized strain of Escherichia coli some 15-fold over levels found in the wild-type strain. By using this strain, the enzyme has been purified approximately 2,000-fold compared with wild type, and various kinetic parameters of the purified enzyme have been studied. In contrast to previous reports, the inhibition by phenylalanine was found to exhibit sigmoidal kinetics, suggestive of cooperative interactions between phenylalanine binding sites. Stimulation of enzyme activity by Co(2+) was minimal (14%).