A hydrogenase is an enzyme that catalyses the reversible oxidation of molecular hydrogen (H₂). Hydrogenases play a vital role in anaerobic metabolism. Ribbon diagram of the catalytically perfect enzyme TIM. An enzyme is a protein that catalyzes, or speeds up, a chemical reaction. ... Generic graph showing the effect of a catalyst in an hypotetical exothermic chemical reaction. ... Redox reactions include all chemical processes in which atoms have their oxidation number (oxidation state) changed. ... General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... Glycolysis is a term referring to a series of biochemical reactions by which a molecule of glucose is oxidized to two molecules of pyruvic acid. ...

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 compounds and proteins such as ferredoxins, cytochrome c₃, and cytochrome c₆ can act as physiological electron donors (D) or acceptors (A) for hydrogenases: General Name, Symbol, Number oxygen, O, 8 Chemical series Chalcogens Group, Period, Block 16, 2, p Appearance colorless Atomic mass 15. ... In inorganic chemistry, nitrates are the salts of nitric acid. ... Sulfate is the IUPAC name for the SO42- ion (British English: Sulphate), consisting of a central sulfur atom bonded singly (sigma) to two oxygen atoms and double bonded (sigma and pi) to two oxygen atoms. ... Carbon dioxide is an atmospheric gas comprised of one carbon and two oxygen atoms. ... A fumarate is a salt or ester of fumaric acid. ... Pyruvate (CH3COCOO−) is the ionized form of pyruvic acid. ... Ferredoxin is an electron receptor used in both Cyclic and Non cyclic photophosphorylation. ... Cytochromes are generally membrane-bound proteins that contain heme groups and carry out electron transport or catalyse reductive/oxidative reactions. ...

H₂ + A_ox → 2H⁺ + A_red (1)

2H⁺ + D_red → H₂ + D_ox (2)

Hydrogenases were first discovered in the 1930s, and they have attracted interest from many researchers. The mechanism of the catalysis of hydrogenase might help catalytic scientists to design clean biological energy sources that produce hydrogen molecules.

Biochemical classification

EC 1.12.1.2 hydrogen dehydrogenase (hydrogen:NAD⁺ oxidoreductase) EC numbers (Enzyme Commission numbers) are a numerical classification scheme for enzymes, based on the chemical reactions they catalyze. ...

H₂ + NAD⁺ = H⁺ + NADH

EC 1.12.1.3 hydrogen dehydrogenase (NADP) (hydrogen:NADPH⁺ oxidoreductase)

H₂ + NADP⁺ = H⁺ + NADPH

EC 1.12.2.1 cytochrome-c₃ hydrogenase (hydrogen:ferricytochrome-c₃ oxidoreductase)

2H₂ + ferricytochrome c₃ = 4H⁺ + ferrocytochrome c₃

EC 1.12.7.2 ferredoxin hydrogenase (hydrogen:ferredoxin oxidoreductase)

H₂ + oxidized ferredoxin = 2H⁺ + reduced ferredoxin

EC 1.12.98.1 coenzyme F₄₂₀ hydrogenase (hydrogen:coenzyme F₄₂₀ oxidoreductase)

H₂ + coenzyme F₄₂₀ = reduced coenzyme F₄₂₀

EC 1.12.99.6 hydrogenase (acceptor) (hydrogen:acceptor oxidoreductase)

H₂ + A = AH₂

EC 1.12.5.1 hydrogen:quinone oxidoreductase

H₂ + menaquinone = menaquinol

EC 1.12.98.2 5,10-methenyltetrahydromethanopterin hydrogenase (hydrogen:5,10-methenyltetrahydromethanopterin oxidoreductase)

H₂ + 5,10-methenyltetrahydromethanopterin = H⁺ + 5,10-methylenetetrahydromethanopterin

EC 1.12.98.3 Methanosarcina-phenazine hydrogenase [hydrogen:2-(2,3-dihydropentaprenyloxy)phenazine oxidoreductase]

H₂ + 2-(2,3-dihydropentaprenyloxy)phenazine = 2-dihydropentaprenyloxyphenazine

Structural classification

Until 2004, hydrogenases were classified according to the metals thought to 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. Selenocysteine is an amino acid that is present in several enzymes (for example glutathione peroxidases, tetraiodothyronine 5 deiodinases, thioredoxin reductases, formate dehydrogenases, glycine reductases and some hydrogenases). ...

The Ni-Fe hydrogenases are heterodimeric proteins consisting of small (S) and large (L) subunits. The small subunit contains three iron-sulfur clusters while the large subunit contains a nickel-iron centre. Periplasmic, cytoplasmic, and cytoplasmic membrane-bound hydrogenases have been found. The Ni-Fe hydrogenases, when isolated, are found to catalyse both H₂ evolution and uptake, with low-potential multihaem cytochromes such as cytochrome c₃ acting as either electron donors or acceptors, depending on their oxidation state. An iron-sulfur cluster is a structural motif found in certain metalloproteins, such as the ferredoxins, as well as NADH dehydrogenase and Coenzyme Q - cytochrome c reductase of the electron transfer system. ...

The hydrogenases containing no other metal than iron are called Fe hydrogenases (Fe-Hases) or Fe-only hydrogenases. Three families of Fe-Hases are recognized:

(I) cytoplasmic, soluble, monomeric Fe-Hases, found in strict anaerobes such as Clostridium pasteurianum and Megasphaera elsdenii. They are extremely sensitive to inactivation by dioxygen (O₂) and catalyse both H₂ evolution and uptake.

(II) periplasmic, heterodimeric Fe-Hases from Desulfovibrio spp., which can be purified aerobically and catalyse mainly H₂ oxidation.

(III) soluble, monomeric Fe-Hases, found in chloroplasts of green alga Scenedesmus obliquus, catalyses H₂ evolution. The [Fe₂S₂] ferredoxin functions as natural electron donor linking the enzyme to the photosynthetic electron transport chain.

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. Carbon monoxide, chemical formula CO, is a colourless, odourless, flammable and highly toxic gas. ... A cyanide is any chemical compound that contains the group C≡N, with the carbon atom triple-bonded to the nitrogen atom. ...

5,10-methenyltetrahydromethanopterin hydrogenase (EC 1.12.98.2) found in methanogenic Achaea contains neither nickel nor iron-sulfur clusters but single iron atom with a tightly bound CO ligand. your gay ... Achaea (Greek: , Achaïa; see also List of traditional Greek place names) is a province on the northern coast of the Peloponnese, stretching from the mountain ranges of Erymanthus and Cyllene on the south to a narrow strip of fertile land on the north, bordering the Gulf of Corinth, into...

References

• Adams, M.W.W. and Stiefel, E.I. (1998). Biological hydrogen production: Not so elementary. Science 282: 1842–1843.
• Florin, L., Tsokoglou, A. and Happe, T. (2001). A novel type of iron hydrogenase in the green alga Scenedesmus obliquus is linked to the photosynthetic electron transport chain. J. Biol. Chem. 276: 6125–6132.
• Frey, M. (2002). Hydrogenases: hydrogen-activating enzymes. ChemBioChem 3: 153–160.
• Lyon, E.J., Shima, S., Boecher, R., Thauer, R.K., Grevels, F.-W., Bill, E., Roseboom, W. and Albracht, S.P.J. (2004). Carbon monoxide as an intrinsic ligand to iron in the active site of the iron-sulfur-cluster-free hydrogenase H₂-forming methylenetetrahydromethanopterin dehydrogenase as revealed by infrared spectroscopy. J. Am. Chem. Soc. 126: 14239–14248.
• Nicolet, Y., Piras, C., Legrand, P., Hatchikian, E.C. and Fontecilla-Camps, J.C. (1999). Desulfovibrio desulfuricans iron hydrogenase: the structure shows unusual coordination to an active site Fe binuclear center. Structure Fold. Des. 7: 13–23.
• Nicolet, Y., Lemon, B.J., Fontecilla-Camps, J.C. and Peters, J.W. (2000). A novel FeS cluster in Fe-only hydrogenases. Trends Biochem.Sci. 25: 138–143.
• Peters, J.W., Lanzilotta, W.N., Lemon, B.J. and Seefeldt, L.C. (1998). X-ray crystal structure of the Fe-only hydrogenase (CpI) from Clostridium pasteurianum to 1.8 Å resolution. Science 282: 1853–1858.
• Vignais, P.M., Billoud, B. and Meyer, J. (2001). Classification and phylogeny of hydrogenases. FEMS Microbiol. Rev. 25: 455–501.
• Volbeda, A., Charon, M.-H., Piras, C., Hatchikian, E.C., Frey, M. and Fontecilla-Camps, J.C. (1995). Crystal structure of the nickel-iron hydrogenase from Desulfovibrio gigas. Nature 373: 580–587.

External links

• 1HFE - PDB structure of Fe-only hydrogenase from Desulfovibrio desulfuricans
• 1C4A - PDB structure of Fe-only hydrogenase from Clostridium pasteurianum
• 1UBR - PDB structure of Ni-Fe hydrogenase from Desulfovibrio vulgaris
• 1CC1 - PDB structure of Ni-Fe-Se hydrogenase from Desulfomicrobium baculatum
• Animation - Mechanism of nickel-iron hydrogenase