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Isocitrate dehydrogenase kinase/phosphatase.

D C Laporte1, C S Stueland, T P Ikeda

  • 1Department of Biochemistry, University of Minnesota, Minneapolis 55455.

Biochimie
|September 1, 1989
PubMed
Summary

Escherichia coli uses a unique bifunctional enzyme, isocitrate dehydrogenase (IDH) kinase/phosphatase, to regulate metabolic pathways. This enzyme controls carbon flow through the glyoxylate bypass, crucial for growth on acetate.

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Area of Science:

  • Biochemistry
  • Microbial Metabolism
  • Enzymology

Background:

  • Isocitrate dehydrogenase (IDH) in Escherichia coli is regulated by phosphorylation.
  • This regulation is managed by a single, bifunctional enzyme: IDH kinase/phosphatase, encoded by the aceK gene.
  • The enzyme's sequence lacks typical protein kinase features but possesses an ATP binding site.

Purpose of the Study:

  • To elucidate the mechanism of IDH phosphorylation and dephosphorylation.
  • To understand the role of IDH kinase/phosphatase in controlling metabolic flux.
  • To investigate how IDH kinase/phosphatase responds to general metabolic signals.

Main Methods:

  • Analysis of the bifunctional nature of IDH kinase/phosphatase.
  • Investigation of the IDH phosphorylation/dephosphorylation cycle.
  • Assessment of the enzyme's response to varying metabolite levels and IDH overproduction.

Main Results:

  • IDH kinase and phosphatase activities likely occur at the same active site, coupled with ATP hydrolysis.
  • The IDH phosphorylation cycle regulates isocitrate flux through the glyoxylate bypass, essential for acetate metabolism.
  • IDH kinase/phosphatase responds to diverse metabolites, modulating its kinase and phosphatase activities.

Conclusions:

  • The IDH phosphorylation cycle, mediated by IDH kinase/phosphatase, is a key metabolic control mechanism in E. coli.
  • The enzyme's ability to sense general metabolism allows for robust adaptation to metabolic perturbations.
  • Cellular levels of IDH kinase/phosphatase are in excess for steady-state growth but can become rate-limiting during carbon source shifts.

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