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Purification and Properties of 3-Deoxy-D-Arabinoheptulosonic Acid-7-Phosphate Synthetase (trp) from Escherichia coli

^a School of Microbiology, University of Melbourne, Parkville, Victoria, Australia

ABSTRACT

The 3-deoxy-D-arabinoheptulosonic acid-7-phosphate synthetase which is subject to regulation by tryptophan has been partially purified from a strain of Escherichia coli K-12, in which this is the only functional form of this enzyme activity, and from a similar strain possessing a feedback-resistant form of the enzyme. Maximal observed inhibition by tryptophan of the feedback-sensitive enzyme was 56%. There was no evidence for cooperativity in the saturation of the enzyme with tryptophan or E4P. The molecular weights of the feedback-sensitive and feedback-resistant forms of the enzyme were the same (52,000), and no change was detected in the molecular weight of the feedback-sensitve enzyme in the presence of tryptophan. The effect of tryptophan analogues was tested to determine the nature of the tryptophan binding site. Treatment with ethylenediaminetetraacetic acid removed 80% of the activity of the feedback-sensitive enzyme. This activity was restored upon the addition of Co²⁺ or Mn²⁺. Neither treatment with ethylenediaminetetraacetic acid nor addition of Co²⁺ or Mn²⁺ affected the activity of the feedback-resistant enzyme.

¹ Present address: Walter & Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia

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