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Hydrogen uptake (H2 oxidation) (1) is coupled to the reduction of electron acceptors such as oxygen, nitrate, sulfate, carbon dioxide, and fumarate, whereas proton reduction (H2 evolution) (2) is essential in pyruvate fermentation and in the disposal of excess electrons. Both low-molecular weight compounds and proteins such as ferredoxins, cytochrome c3, and cytochrome c6 can act as physiological electron donors (D) or acceptors (A) for hydrogenases:
Hydrogenases were first discovered in the 1930s, and they have since attracted interest from many researchers including inorganic chemists who have synthesized a variety of hydrogenase mimics. Understanding the catalytic mechanism of hydrogenase might help scientists design clean biological energy sources, such as algae, that produce hydrogen...
EC 22.214.171.124 hydrogen dehydrogenase (hydrogen:NAD+ oxidoreductase)
EC 126.96.36.199 hydrogen dehydrogenase (NADP) (hydrogen:NADPH+ oxidoreductase)
EC 188.8.131.52 cytochrome-c3 hydrogenase (hydrogen:ferricytochrome-c3 oxidoreductase)
EC 184.108.40.206 ferredoxin hydrogenase (hydrogen:ferredoxin oxidoreductase)
EC 220.127.116.11 coenzyme F420 hydrogenase (hydrogen:coenzyme F420 oxidoreductase)
EC 18.104.22.168 hydrogenase (acceptor) (hydrogen:acceptor oxidoreductase)
EC 22.214.171.124 hydrogen:quinone oxidoreductase
EC 126.96.36.199 5,10-methenyltetrahydromethanopterin hydrogenase (hydrogen:5,10-methenyltetrahydromethanopterin oxidoreductase)
EC 188.8.131.52 Methanosarcina-phenazine hydrogenase [hydrogen:2-(2,3-dihydropentaprenyloxy)phenazine oxidoreductase]
Until 2004, hydrogenases were classified according to the metals thought to be at their active sites; three classes were recognized: iron-only (Fe-only), nickel-iron (NiFe), and "metal-free". In 2004, Thauer et al. showed that the metal-free hydrogenases in fact contain iron. Thus, those enzymes previously called "metal-free" are now named "FeS-free", since this protein contains no inorganic sulfide in contrast to the Fe-only enzymes. In some Ni-Fe hydrogenases, one of the Ni-bound cysteine residues is replaced by selenocysteine. On the basis of sequence similarity, however, the Ni-Fe and Ni-Fe-Se hydrogenases should be considered a single superfamily.
Ni-Fe and Fe-only hydrogenases have some common features in their structures: each enzyme has an active site and a few Fe-S clusters that are buried in protein. The active site, which is believed to be the place where catalysis takes place, is also a metallocluster, and each metal is coordinated by carbon monoxide (CO) and cyanide (CN-) ligands.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Hydrogenase". A list of authors is available in Wikipedia.|