A Bacterial Electron-bifurcating Hydrogenase

• Published in: The Journal of biological chemistry Vol. 287; no. 37; pp. 31165 - 31171
• Main Authors: Schuchmann, Kai, Müller, Volker
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 07.09.2012; American Society for Biochemistry and Molecular Biology
• Subjects: Acetobacterium - enzymology; Acetogenesis; Adenosine Triphosphate - chemistry; Adenosine Triphosphate - metabolism; Bacterial Proteins - chemistry; Bacterial Proteins - isolation & purification; Bacterial Proteins - metabolism; Bioenergetics; Catalytic Domain; Electron Bifurcation; Electron Transport; Enzyme Mechanisms; Ferredoxins - chemistry; Ferredoxins - metabolism; Hydrogen - chemistry; Hydrogen - metabolism; Hydrogenase; Hydrogenase - chemistry; Hydrogenase - isolation & purification; Hydrogenase - metabolism; Iron-Sulfur Protein; Metabolism; Metalloenzymes; Microbiology; Oxidation-Reduction; Enzyme Mechanisms; Hydrogenase; Electron Transport; Bioenergetics; Microbiology; Acetogenesis; Iron-Sulfur Protein; Metabolism; Metalloenzymes; Electron Bifurcation
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M112.395038

The Wood-Ljungdahl pathway of anaerobic CO2 fixation with hydrogen as reductant is considered a candidate for the first life-sustaining pathway on earth because it combines carbon dioxide fixation with the synthesis of ATP via a chemiosmotic mechanism. The acetogenic bacterium Acetobacterium woodii uses an ancient version of the pathway that has only one site to generate the electrochemical ion potential used to drive ATP synthesis, the ferredoxin-fueled, sodium-motive Rnf complex. However, hydrogen-based ferredoxin reduction is endergonic, and how the steep energy barrier is overcome has been an enigma for a long time. We have purified a multimeric [FeFe]-hydrogenase from A. woodii containing four subunits (HydABCD) which is predicted to have one [H]-cluster, three [2Fe2S]-, and six [4Fe4S]-clusters consistent with the experimental determination of 32 mol of Fe and 30 mol of acid-labile sulfur. The enzyme indeed catalyzed hydrogen-based ferredoxin reduction, but required NAD+ for this reaction. NAD+ was also reduced but only in the presence of ferredoxin. NAD+ and ferredoxin reduction both required flavin. Spectroscopic analyses revealed that NAD+ and ferredoxin reduction are strictly coupled and that they are reduced in a 1:1 stoichiometry. Apparently, the multimeric hydrogenase of A. woodii is a soluble energy-converting hydrogenase that uses electron bifurcation to drive the endergonic ferredoxin reduction by coupling it to the exergonic NAD+ reduction. Background: Hydrogen-dependent reduction of ferredoxin, a common “low-redox potential” electron carrier in anaerobes, is a highly endergonic reaction. Results: The [FeFe]-hydrogenase from an acetogenic bacterium strictly requires NAD+ for ferredoxin reduction and reduces NAD+ and ferredoxin simultaneously. Conclusion: The [FeFe]-hydrogenase drives ferredoxin reduction at the expense of exergonic NAD+ reduction. Significance: The [FeFe]-hydrogenase uses electron bifurcation for energy coupling.