title: Coupled ferredoxin and crotonyl coenzyme A (CoA) reduction with NADH catalyzed by the butyryl-CoA dehydrogenase/Etf complex from Clostridium kluyveri.
abstract: 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.
authors.affiliation: Max Planck Institute for Terrestrial Microbiology, Marburg, Germany.
authors.forename: Fuli
authors.initials: F
authors.lastname: Li
authors.forename: Julia
authors.initials: J
authors.lastname: Hinderberger
authors.forename: Henning
authors.initials: H
authors.lastname: Seedorf
authors.forename: Jin
authors.initials: J
authors.lastname: Zhang
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Buckel
authors.forename: Rudolf K
authors.initials: RK
authors.lastname: Thauer
mesh_terms: D000214:Acyl Coenzyme A / Q000378:metabolism*; D044926:Butyryl-CoA Dehydrogenase / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D002384:Catalysis; D047010:Clostridium kluyveri / Q000201:enzymology* / Q000254:growth & development; D044927:Electron-Transferring Flavoproteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D005288:Ferredoxins / Q000378:metabolism*; D006859:Hydrogen / Q000378:metabolism; D009243:NAD / Q000378:metabolism*; D010084:Oxidation-Reduction
chemical_list: D000214:Acyl Coenzyme A; D044927:Electron-Transferring Flavoproteins; D005288:Ferredoxins; D009243:NAD; D006859:Hydrogen; C010701:crotonyl-coenzyme A; D044926:Butyryl-CoA Dehydrogenase