TY  - JOUR
A1  - Hess, Verena
A1  - Schuchmann, Kai
A1  - Müller, Volker
T1  - The ferredoxin:NAD+ oxidoreductase (Rnf) from the acetogen Acetobacterium woodii requires Na+ and is reversibly coupled to the membrane potential
T2  - Journal of biological chemistry
N2  - 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.
KW  - Bioenergetics/Electron Transfer Complex
KW  - Electron Transfer
KW  - Energy Metabolism
KW  - Enzyme Kinetics
KW  - Membrane Energetics
KW  - Membrane Transport
KW  - Oxidation-Reduction
KW  - Physiology
KW  - Sodium Transport
KW  - Rnf
Y1  - 2021
UR  - http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/75888
UR  - https://nbn-resolving.org/urn:nbn:de:hebis:30:3-758880
SN  - 0021-9258
VL  - 288
IS  - 44
SP  - 31496
EP  - 31502
PB  - American Society for Biochemistry and Molecular Biology Publications
CY  - Bethesda, Md
ER  -