The Feedback Control Mechanism of Biosynthetic L-Threonine Deaminase by L-Isoleucine

  1. Jean-Pierre Changeux
  1. Service de Biochimie Cellulaire, Institut Pasteur, Paris, France

This extract was created in the absence of an abstract.

Excerpt

“Man does not realize how that which varies is a unity. There is a harmony of opposite tensions as there is one of bow and lyre.”

Heraclitus the Obscure.

I. INTRODUCTION

As has been extensively discussed in other reports of this Symposium, the biosynthesis of metabolites in microorganisms is controlled by negative feedback mechanisms. In the case of feedback inhibition the end-product competitively inhibits the activity of the first specific enzyme of a chain—and consequently blocks the enzymatic processes leading to its own synthesis. Before the discovery of such regulatory enzymes, only analogues of substrates were known as competitive inhibitors. Thus the problem arose: how can a compound with a structure very dissimilar from that of its substrate act as a competitive inhibitor of an enzyme?

Our investigation concerns the first enzyme specifically involved by Escherichia coli K12 in the biosynthesis of isoleucine: L-threonine deaminase, which converts L-threonine into α-ketobutyric...

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