MetaCyc Polypeptide: Ech hydrogenase subunit B

Gene: echB Accession Number: G-12634 (MetaCyc)

Synonyms: Mbar_A0151

Species: Caldanaerobacter subterraneus tengcongensis

Component of: ech hydrogenase (extended summary available)

membrane bound subunit.

Molecular Weight of Polypeptide: 24.0 kD (experimental)

Unification Links: String:269797.Mbar_A0151 , UniProt:Q46G56

Relationship Links: Entrez-gene:Homolog:AAZ69136 , InterPro:IN-FAMILY:IPR001694 , Panther:IN-FAMILY:PTHR11432 , Pfam:IN-FAMILY:PF00146

Gene-Reaction Schematic: ?

Gene-Reaction Schematic

Created 17-Mar-2011 by Weerasinghe D , SRI International

Subunit of: ech hydrogenase

Synonyms: Mbh hydrogenase, ferredoxin hydrogenase

Species: Caldanaerobacter subterraneus tengcongensis

Subunit composition of ech hydrogenase = [EchF][EchE][EchD][EchC][EchB][EchA]
         Ech hydrogenase subunit F = EchF (summary available)
         Ech hydrogenase subunit E = EchE (summary available)
         Ech hydrogenase subunit D = EchD (summary available)
         Ech hydrogenase subunit C = EchC (summary available)
         Ech hydrogenase subunit B = EchB (summary available)
         Ech hydrogenase subunit A = EchA (summary available)


Hydrogenases are found in a variety of microorganisms and catalyze the reversible reaction of proton reduction to H2 formation [Ducat11]. This enables some organisms to use H2 as a source of reducing equivalents under both aerobic and anaerobic conditions, while in other organisms the enzyme reduces protons to H2, thereby releasing reducing equivalents obtained from the anaerobic degradation of organic substrates.

[NiFe] hydrogenases are well characterized enzymes that have play a vital role in H2 metabolism [Hedderich04]. A subset of [NiFe] hydrogenases are multisubunit membrane-bound enzyme complexes. They consist of at least four hydrophilic and two integral membrane subunits which form the core of the complex [Hedderich04]. They have closely related counterparts in energy-conserving NADH:quinone oxidoreductase (complex I), which pumps protons across the inner membrane of mitochondria or the plasma membrane of many bacteria [Hedderich05]. Complex I catalyzes electron transfer from NADH to quinone or menaquinone and couples this to the translocation of H+ or sodium ions across a membrane.

The reaction catalyzed by the hydrogenases is significantly different from the reaction catalyzed by complex I. They can utilize electrons derived from reduced ferredoxins or polyferredoxins to catalyze the reduction of H+ [Hedderich05]. This exergonic reaction is coupled to energy conservation via electron-transport phosphorylation. In a reaction driven by reverse electron transport, other family members of this hydrogenase can provide the cell with reduced ferredoxin using H2 as the electron donor [Hedderich05].

About This Enzyme

The [NiFe] hydrogenase is ferredoxin dependent, and is composed of 6 subunits. The enzyme has a high degree of homology with 6 subunits of ech hydrogenase from the methanogenic archaeon Methanosarcina barkeri [Soboh04]. Adjacent to the ech operon, Caldanaerobacter subterraneus tengcongensis has a second gene cluster designated hyp, which encodes all proteins essential for the biosynthesis of the [NiFe] centres, but not for the protease that catalyzes the C-terminal processing of the hydrogenase large subunit (EchE) [Soboh04]. Other [NiFe] hydrogenases have a carboxy terminal extension on the hydrogenase large subunit that is cleaved off after the correct insertion of the [NiFe] centre, which is not present in EchE of both Caldanaerobacter subterraneus tengcongensis and Methanosarcina barkeri [Blokesch02a].

Membrane bound hydrogenases catalyze the reduction of H+ with electrons derived from reduced ferredoxins and this exergonic reaction is coupled to to energy conservation via electron transport phosphorylation [Hedderich05]. Therefore, these enzymes have been designated energy-converting [NiFe] hydrogenases (Ech) [Vignais01]. Pyrococcus furiosus has such a membrane bound (Mbh) hydrogenase as does Caldanaerobacter subterraneus tengcongensis that mediates H2 production [Sapra03].

Caldanaerobacter subterraneus tengcongensis uses the enzymes of the glycolysis III (from glucose) pathway to convert glucose to pyruvate, generating ATP and NADH. Pyruvate is then oxidized to acetyl-CoA and CO2 using the pyruvate fermentation to acetate and lactate II pathway, thus generating reduced ferredoxin via pyruvate:ferredoxin oxidoreductase.

Molecular Weight: 188.0 kD (experimental) [Soboh04]

Created 17-Mar-2011 by Weerasinghe D , SRI International

Enzymatic reaction of: hydrogenase

EC Number:

2 an oxidized ferredoxin + H2 <=> 2 a reduced ferredoxin + 2 H+

The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the direction in which it was curated.

This reaction is reversible.

In Pathways: superpathway of hydrogen production , hydrogen production III

Kinetic Parameters:

Km (μM)
an oxidized ferredoxin
a reduced ferredoxin


Blokesch02a: Blokesch M, Paschos A, Theodoratou E, Bauer A, Hube M, Huth S, Bock A (2002). "Metal insertion into NiFe-hydrogenases." Biochem Soc Trans 30(4);674-80. PMID: 12196162

Ducat11: Ducat DC, Sachdeva G, Silver PA (2011). "Rewiring hydrogenase-dependent redox circuits in cyanobacteria." Proc Natl Acad Sci U S A 108(10);3941-6. PMID: 21368150

Hedderich04: Hedderich R (2004). "Energy-converting [NiFe] hydrogenases from archaea and extremophiles: ancestors of complex I." J Bioenerg Biomembr 36(1);65-75. PMID: 15168611

Hedderich05: Hedderich R, Forzi L (2005). "Energy-converting [NiFe] hydrogenases: more than just H2 activation." J Mol Microbiol Biotechnol 10(2-4);92-104. PMID: 16645307

Park06: Park YJ, Yoo CB, Choi SY, Lee HB (2006). "Purifications and characterizations of a ferredoxin and its related 2-oxoacid:ferredoxin oxidoreductase from the hyperthermophilic archaeon, Sulfolobus solfataricus P1." J Biochem Mol Biol 39(1);46-54. PMID: 16466637

Sapra03: Sapra R, Bagramyan K, Adams MW (2003). "A simple energy-conserving system: proton reduction coupled to proton translocation." Proc Natl Acad Sci U S A 100(13);7545-50. PMID: 12792025

Soboh04: Soboh B, Linder D, Hedderich R (2004). "A multisubunit membrane-bound [NiFe] hydrogenase and an NADH-dependent Fe-only hydrogenase in the fermenting bacterium Thermoanaerobacter tengcongensis." Microbiology 150(Pt 7);2451-63. PMID: 15256587

Vignais01: Vignais PM, Billoud B, Meyer J (2001). "Classification and phylogeny of hydrogenases." FEMS Microbiol Rev 25(4);455-501. PMID: 11524134

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Please cite the following article in publications resulting from the use of MetaCyc: Caspi et al, Nucleic Acids Research 42:D459-D471 2014
Page generated by SRI International Pathway Tools version 19.0 on Tue Oct 13, 2015, biocyc13.