title: NADP+ reduction with reduced ferredoxin and NADP+ reduction with NADH are coupled via an electron-bifurcating enzyme complex in Clostridium kluyveri.
abstract: It was recently found that the cytoplasmic butyryl-coenzyme A (butyryl-CoA) dehydrogenase-EtfAB complex from Clostridium kluyveri couples the exergonic reduction of crotonyl-CoA to butyryl-CoA with NADH and the endergonic reduction of ferredoxin with NADH via flavin-based electron bifurcation. We report here on a second cytoplasmic enzyme complex in C. kluyveri capable of energetic coupling via this novel mechanism. It was found that the purified iron-sulfur flavoprotein complex NfnAB couples the exergonic reduction of NADP+ with reduced ferredoxin (Fdred) and the endergonic reduction of NADP+ with NADH in a reversible reaction: Fdred2-+NADH+2 NADP++H+=Fdox+NAD++2 NADPH. The role of this energy-converting enzyme complex in the ethanol-acetate fermentation of C. kluyveri is discussed.
authors.affiliation: Max Planck Institute for Terrestrial Microbiology, Marburg, Germany; State Key Laboratory of Microbial Technology, Shandong University, Jinan, People’s Republic of
authors.forename: Shuning
authors.initials: S
authors.lastname: Wang
authors.forename: Haiyan
authors.initials: H
authors.lastname: Huang
authors.forename: Johanna
authors.initials: J
authors.lastname: Moll
authors.forename: Rudolf K
authors.initials: RK
authors.lastname: Thauer
mesh_terms: D000214:Acyl Coenzyme A / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D047010:Clostridium kluyveri / Q000201:enzymology* / Q000235:genetics; D005288:Ferredoxins / Q000378:metabolism*; D009243:NAD / Q000378:metabolism*; D009249:NADP / Q000378:metabolism*; D010084:Oxidation-Reduction
chemical_list: D000214:Acyl Coenzyme A; D001426:Bacterial Proteins; D005288:Ferredoxins; D009243:NAD; C024343:butyryl-coenzyme A; D009249:NADP; C010701:crotonyl-coenzyme A