|Gene:||echB||Accession Number: G-12634 (MetaCyc)|
Component of: ech hydrogenase (extended summary available)
membrane bound subunit.
Molecular Weight of Polypeptide: 24.0 kD (experimental)
Subunit of: ech hydrogenase
Synonyms: Mbh hydrogenase, ferredoxin hydrogenase
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]
Enzymatic reaction of: hydrogenase
EC Number: 18.104.22.168
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.
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
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
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