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Journal of Bacteriology, February 2008, p. 843-850, Vol. 190, No. 3
0021-9193/08/$08.00+0     doi:10.1128/JB.01417-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Coupled Ferredoxin and Crotonyl Coenzyme A (CoA) Reduction with NADH Catalyzed by the Butyryl-CoA Dehydrogenase/Etf Complex from Clostridium kluyveri ^,

Fuli Li,^1, Julia Hinderberger,^1, Henning Seedorf,¹ Jin Zhang,² Wolfgang Buckel,² and Rudolf K. Thauer^1*

Max Planck Institute for Terrestrial Microbiology, D-35043 Marburg, Germany,¹ Laboratorium für Mikrobiologie, Fachbereich Biologie, Philipps-Universität, D-35032 Marburg, Germany²

Received 31 August 2007/ Accepted 26 October 2007

Cell extracts of butyrate-forming clostridia have been shown to catalyze acetyl-coenzyme A (acetyl-CoA)- and ferredoxin-dependent formation of H₂ from NADH. It has been proposed that these bacteria contain an NADH:ferredoxin oxidoreductase which is allosterically regulated by acetyl-CoA. We report here that ferredoxin reduction with NADH in cell extracts from Clostridium kluyveri is catalyzed by the butyryl-CoA dehydrogenase/Etf complex and that the acetyl-CoA dependence previously observed is due to the fact that the cell extracts catalyze the reduction of acetyl-CoA with NADH via crotonyl-CoA to butyryl-CoA. The cytoplasmic butyryl-CoA dehydrogenase complex was purified and is shown to couple the endergonic reduction of ferredoxin (E₀' = –410 mV) with NADH (E₀' = –320 mV) to the exergonic reduction of crotonyl-CoA to butyryl-CoA (E₀' = –10 mV) with NADH. The stoichiometry of the fully coupled reaction is extrapolated to be as follows: 2 NADH + 1 oxidized ferredoxin + 1 crotonyl-CoA = 2 NAD⁺ + 1 ferredoxin reduced by two electrons + 1 butyryl-CoA. The implications of this finding for the energy metabolism of butyrate-forming anaerobes are discussed in the accompanying paper.

Published ahead of print on 9 November 2007.

Dedicated to Karl Decker, Emeritus Professor of Biochemistry, University Freiburg, Freiburg, Germany.

F.L. and J.H. contributed equally to this work.

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