The ferredoxin:NAD+ oxidoreductase (Rnf) from the acetogen Acetobacterium woodii requires Na+ and is reversibly coupled to the membrane potential

  • The anaerobic acetogenic bacterium Acetobacterium woodii has a novel Na(+)-translocating electron transport chain that couples electron transfer from reduced ferredoxin to NAD(+) with the generation of a primary electrochemical Na(+) potential across its cytoplasmic membrane. In previous assays in which Ti(3+) was used to reduce ferredoxin, Na(+) transport was observed, but not a Na(+) dependence of the electron transfer reaction. Here, we describe a new biological reduction system for ferredoxin in which ferredoxin is reduced with CO, catalyzed by the purified acetyl-CoA synthase/CO dehydrogenase from A. woodii. Using CO-reduced ferredoxin, NAD(+) reduction was highly specific and strictly dependent on ferredoxin and occurred at a rate of 50 milliunits/mg of protein. Most important, this assay revealed for the first time a strict Na(+) dependence of this electron transfer reaction. The Km was 0.2 mm. Na(+) could be partly substituted by Li(+). Na(+) dependence was observed at neutral and acidic pH values, indicating the exclusive use of Na(+) as a coupling ion. Electron transport from reduced ferredoxin to NAD(+) was coupled to electrogenic Na(+) transport, indicating the generation of ΔμNa(+). Vice versa, endergonic ferredoxin reduction with NADH as reductant was possible, but only in the presence of ΔμNa(+), and was accompanied by Na(+) efflux out of the vesicles. This is consistent with the hypothesis that Rnf also catalyzes ferredoxin reduction at the expense of an electrochemical Na(+) gradient. The physiological significance of this finding is discussed. Background: Ferredoxin:NAD+-oxidoreductases (Rnf) found in many bacteria are novel ion-translocating electron transport chains. Results: A Na+ requirement for the reaction and its reversible coupling to the transmembrane Na+ gradient are demonstrated. Conclusion: Na+ is the coupling ion. Rnf not only generates a Na+ potential but also uses it to drive the reverse reaction. Significance: Evidence for a function of Rnf in ferredoxin reduction is provided.

Download full text files

Export metadata

Additional Services

Share in Twitter Search Google Scholar
Author:Verena HessORCiDGND, Kai SchuchmannGND, Volker MüllerORCiD
Pubmed Id:
Parent Title (English):Journal of biological chemistry
Publisher:American Society for Biochemistry and Molecular Biology Publications
Place of publication:Bethesda, Md
Document Type:Article
Date of Publication (online):2021/01/04
Year of first Publication:2013
Publishing Institution:Universitätsbibliothek Johann Christian Senckenberg
Release Date:2023/11/15
Tag:Bioenergetics/Electron Transfer Complex; Electron Transfer; Energy Metabolism; Enzyme Kinetics; Membrane Energetics; Membrane Transport; Oxidation-Reduction; Physiology; Rnf; Sodium Transport
Page Number:7
First Page:31496
Last Page:31502
Dewey Decimal Classification:5 Naturwissenschaften und Mathematik / 57 Biowissenschaften; Biologie / 570 Biowissenschaften; Biologie
Licence (German):License LogoCreative Commons - CC BY - Namensnennung 4.0 International