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Role of Reduced Coenzymes NADH and FADH₂01:29

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An electron-bifurcating caffeyl-CoA reductase.

Johannes Bertsch1, Anutthaman Parthasarathy, Wolfgang Buckel

  • 1Department of Molecular Microbiology and Bioenergetics, Institute of Molecular Biosciences, Johann Wolfgang Goethe-Universität Frankfurt am Main, 60438 Frankfurt, Germany.

The Journal of Biological Chemistry
|March 13, 2013
PubMed
Summary

Acetobacterium woodii uses a novel electron bifurcation mechanism to reduce ferredoxin, an essential energy coupling step. This process couples NADH-dependent caffeyl-CoA reduction to ferredoxin reduction, fueling bioenergetics.

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Published on: May 22, 2016

Area of Science:

  • Microbiology
  • Biochemistry
  • Bioenergetics

Background:

  • Acetogenic bacteria like Acetobacterium woodii utilize ferredoxin (E0' ≈ -500 mV) for energy coupling via the Rnf complex.
  • Ferredoxin reduction is endergonic, requiring coupling to an exergonic reaction for physiological function.
  • NADH-dependent caffeyl-CoA reduction is a potential exergonic reaction to drive ferredoxin reduction.

Purpose of the Study:

  • To investigate the mechanism of ferredoxin reduction in Acetobacterium woodii.
  • To identify and characterize the enzyme complex responsible for coupling NADH oxidation to ferredoxin reduction.
  • To elucidate the role of caffeyl-CoA reductase and electron transfer flavoprotein in this process.

Main Methods:

  • Purification of a multi-subunit enzyme complex containing caffeyl-CoA reductase and electron transfer flavoprotein from A. woodii.
  • Biochemical assays to determine enzyme activity using various electron donors and acceptors.
  • Spectroscopic analysis to monitor electron transfer and determine reaction stoichiometry.
  • Bioinformatic analysis of the carCDE genes encoding the enzyme complex.

Main Results:

  • A purified complex containing caffeyl-CoA reductase and electron transfer flavoprotein was obtained.
  • The complex contains FAD and [4Fe-4S] clusters, confirmed by cofactor analysis.
  • The enzyme complex catalyzed NADH-dependent caffeyl-CoA reduction, which was stimulated by ferredoxin.
  • Spectroscopic data indicated simultaneous reduction of ferredoxin and caffeyl-CoA, with a stoichiometry of 1.3:1.

Conclusions:

  • The caffeyl-CoA reductase-Etf complex from A. woodii employs flavin-dependent electron bifurcation.
  • This novel mechanism couples the exergonic NADH-dependent caffeyl-CoA reduction to the endergonic ferredoxin reduction.
  • This process is crucial for fueling the Rnf complex and driving bioenergetics in A. woodii.