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Journal of Bacteriology, July 2009, p. 4451-4457, Vol. 191, No. 13
0021-9193/09/$08.00+0     doi:10.1128/JB.01582-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

The Iron-Hydrogenase of Thermotoga maritima Utilizes Ferredoxin and NADH Synergistically: a New Perspective on Anaerobic Hydrogen Production ^,

Gerrit J. Schut and Michael W. W. Adams^*

Department of Biochemistry and Molecular Biology, University of Georgia, Athens, Georgia 30602-7229

Received 8 November 2008/ Accepted 23 April 2009

The hyperthermophilic and anaerobic bacterium Thermotoga maritima ferments a wide variety of carbohydrates, producing acetate, CO₂, and H₂. Glucose is degraded through a classical Embden-Meyerhof pathway, and both NADH and reduced ferredoxin are generated. The oxidation of these electron carriers must be coupled to H₂ production, but the mechanism by which this occurs is unknown. The trimeric [FeFe]-type hydrogenase that was previously purified from T. maritima does not use either reduced ferredoxin or NADH as a sole electron donor. This problem has now been resolved by the demonstration that this hydrogenase requires the presence of both electron carriers for catalysis of H₂ production. The enzyme oxidizes NADH and ferredoxin simultaneously in an approximately 1:1 ratio and in a synergistic fashion to produce H₂. It is proposed that the enzyme represents a new class of bifurcating [FeFe] hydrogenase in which the exergonic oxidation of ferredoxin (midpoint potential, –453 mV) is used to drive the unfavorable oxidation of NADH (E₀' = –320 mV) to produce H₂ (E₀' = –420 mV). From genome sequence analysis, it is now clear that there are two major types of [FeFe] hydrogenases: the trimeric bifurcating enzyme and the more well-studied monomeric ferredoxin-dependent [FeFe] hydrogenase. Almost one-third of the known H₂-producing anaerobes appear to contain homologs of the trimeric bifurcating enzyme, although many of them also harbor one or more homologs of the simpler ferredoxin-dependent hydrogenase. The discovery of the bifurcating hydrogenase gives a new perspective on our understanding of the bioenergetics and mechanism of H₂ production and of anaerobic metabolism in general.

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* Corresponding author. Mailing address: Department of Biochemistry and Molecular Biology, Davison Life Sciences Complex, University of Georgia, Athens, GA 30602-7229. Phone: (706) 542-2060. Fax: (706) 542-0229. E-mail: adams{at}bmb.uga.edu

Published ahead of print on 1 May 2009.

Supplemental material for this article may be found at http://jb.asm.org/.

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Journal of Bacteriology, July 2009, p. 4451-4457, Vol. 191, No. 13
0021-9193/09/$08.00+0     doi:10.1128/JB.01582-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

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