Studies on the catalytic mechanism of H2-forming methylenetetrahydromethanopterin dehydrogenase: para-ortho H2 conversion rates in H2O and D2O

Hartmann, Gudrun C.; Santamaria, Elena; Fernández, Vı́ctor M.; Thauer, Rudolf K.

doi:10.1007/s007750050077

Cited by 34 publications

(31 citation statements)

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“…However, results from several biochemical studies indicate H 2 hydrogen is added to the carbon atom directly during at-least one step of metabolism (step 4, Fig. 8; Schworer et al, 1993;Schleucher et al, 1994;Klein et al, 1995a,b;Hartmann et al, 1996). Results from this study and from Daniels et al (1980) do Fig.…”

Section: The Source Of Ch 4 -Bound Hydrogenmentioning

confidence: 46%

“…This enzyme catalyzes the heterolytic cleavage of H 2 and the subsequent hydride shift to a conjugated carbocation reaction center (Schleucher et al, 1994;Klein et al, 1995b;Hartmann et al, 1996;. Hydrogen from H 2 is affixed directly to the growing methane moiety, though isotope exchange occurs (Schworer et al, 1993;Klein et al, 1995a,b;Hartmann et al, 1996).…”

Section: 222mentioning

confidence: 98%

See 1 more Smart Citation

Carbon and hydrogen isotope fractionation by moderately thermophilic methanogens 1 1Associate editor: N. E. Ostrom

Valentine

Chidthaisong²,

Rice

et al. 2004

Geochimica et Cosmochimica Acta

307

335

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Section: The Source Of Ch 4 -Bound Hydrogenmentioning

confidence: 46%

Section: 222mentioning

confidence: 98%

Carbon and hydrogen isotope fractionation by moderately thermophilic methanogens 1 1Associate editor: N. E. Ostrom

Valentine

Chidthaisong²,

Rice

et al. 2004

Geochimica et Cosmochimica Acta

307

335

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“…Para-ortho hydrogen conversion was measured as described (37). Molecular hydrogen consisting of 50% para hydrogen and 50% ortho hydrogen was prepared as described by Hartman et al (38).…”

Section: Bacterial Strains Plasmids and Growth Conditionsmentioning

confidence: 99%

A Glutamate Is the Essential Proton Transfer Gate during the Catalytic Cycle of the [NiFe] Hydrogenase

Dementin

Burlat

Lacey

et al. 2004

Journal of Biological Chemistry

140

185

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Kinetic, EPR, and Fourier transform infrared spectroscopic analysis of Desulfovibrio fructosovorans [NiFe]hydrogenase mutants targeted to Glu-25 indicated that this amino acid participates in proton transfer between the active site and the protein surface during the catalytic cycle. Replacement of that glutamic residue by a glutamine did not modify the spectroscopic properties of the enzyme but cancelled the catalytic activity except the para-H 2 /ortho-H 2 conversion. This mutation impaired the fast proton transfer from the active site that allows high turnover numbers for the oxidation of hydrogen. Replacement of the glutamic residue by the shorter aspartic acid slowed down this proton transfer, causing a significant decrease of H 2 oxidation and hydrogen isotope exchange activities, but did not change the para-H 2 /ortho-H 2 conversion activity. The spectroscopic properties of this mutant were totally different, especially in the reduced state in which a non-photosensitive nickel EPR spectrum was obtained.Many microorganisms use molecular hydrogen in their metabolic routes as an energy source or for evacuating an excess of electrons. The enzymes that catalyze reversibly the conversion of molecular hydrogen to two electrons and two protons are known as hydrogenases. Although this is the simplest chemical reaction, the catalytic mechanism of these enzymes is quite complicated, and its details are still a matter of debate (1). Hydrogen isotope exchange experiments indicate that the H 2 cleavage reaction is heterolytic; thus, a hydride and a proton are formed in the first step (2, 3). In the second step, the two electrons of the hydride are extracted, and a second proton is formed. Subsequently, the two electrons have to be transported, via the intramolecular electron transfer chain, from the active site to the redox partner of the hydrogenase (a redox protein or NAD ϩ (P)) in vivo, or a redox dye in vitro; the two protons have to be transferred to the protein environment as well. These steps are reversed in the case of H 2 production activity (1).How do all these steps take place in hydrogenases? These proteins are metalloenzymes that all contain iron, and in many cases, also nickel. The crystallographic structures of several [Fe] hydrogenases (4, 5) and [NiFe] hydrogenases (6, 7) have been obtained by x-ray diffraction studies. In both types of enzymes, the active site is a deeply buried bimetallic center, in which the metals are bridged by thiol groups and have CO and CN Ϫ as ligands. This type of coordination favors the binding of molecular hydrogen or hydride to the active site (1, 8). The crystal structures also indicate that Fe-S clusters are located between the active site and the protein surface, which are thought to form the intramolecular electron pathway in the H 2 production/oxidation mechanism (9). In [NiFe] hydrogenases, one nickel and one iron atom form the bimetallic center. The nickel is coordinated to four cysteine ligands via their thiol groups. Two of them are terminal ligands, and the other...

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“…In contrast to other hydrogenases, Hmd does not catalyze per se the exchange of H 2 with protons of water or the conversion of para-H 2 to ortho-H 2 . Interestingly, these two reactions are, however, mediated in the presence of methenyl-H 4 MPT ϩ (17)(18)(19). The Hmd holoenzyme is composed of two identical subunits of molecular mass 38 kDa and harbors 2 mol of iron per homodimer (14).…”

mentioning

confidence: 99%

The Iron-Sulfur Cluster-free Hydrogenase (Hmd) Is a Metalloenzyme with a Novel Iron Binding Motif

Korbas

Vogt

Meyer‐Klaucke

et al. 2006

Journal of Biological Chemistry

137

162

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The iron-sulfur cluster-free hydrogenase (Hmd) from methanogenic archaea harbors an iron-containing cofactor of yet unknown structure. X-ray absorption spectroscopy of the active, as isolated enzyme from Methanothermobacter marburgensis (mHmd) and of the active, reconstituted enzyme from Methanocaldococcus jannaschii (jHmd) revealed the presence of mononuclear iron with two CO, one sulfur and one or two N/O in coordination distance. In jHmd, the single sulfur ligand is most probably provided by Cys 176 , as deduced from a comparison of the activity and of the x-ray absorption and Mössbauer spectra of the enzyme mutated in any of the three conserved cysteines. In the isolated Hmd cofactor, two CO, one sulfur, and two nitrogen/oxygen atoms coordinate the iron, the sulfur ligand being most probably provided by mercaptoethanol, which is absolutely required for the extraction of the iron-containing cofactor from the holoenzyme and for the stabilization of the extracted cofactor. In active mHmd holoenzyme, the number of iron ligands increased by one when one of the Hmd inhibitors (CO or KCN) were present, indicating that in active Hmd, the iron contains an open coordination site, which is proposed to be the site of H 2 interaction.Hydrogenases are enzymes that catalyze the reversible oxidation of molecular hydrogen (1). Their structure and catalytic mechanism are of considerable applied interest as models for the development of efficient catalysts for hydrogen-fueled processes. Despite intensive efforts, however, the understanding of how hydrogenases react with H 2 is only in its infancy.Two of the three known types of hydrogenases are ironsulfur proteins that contain, besides one or several iron-sulfur clusters, a dinuclear metal center, either [NiFe] or [FeFe], which was shown to be the site of H 2 reaction. Both dinuclear hydrogenases catalyze the reversible formation of 2e Ϫ and 2Hϩ from H 2 , the electrons being transferred one by one to electron acceptors via the iron-sulfur clusters. One iron ion in both dinuclear centers is coordinated by sulfur, CO, and cyanide ligands, as supported by crystal structures of the [NiFe]-hydrogenase (2, 3) and of the [FeFe]-hydrogenase (4 -7). During the catalytic cycle, the iron ion in the [NiFe] center remains in a low spin ferrous state and is not redoxactive (8, 9). In the case of the [FeFe]-hydrogenases, the oxidation states of the dinuclear iron center are still under discussion; however, the involvement of a low spin Fe(II) has been predicted based on the spectroscopic and DFT studies (9 -11). Despite similarities in structures and properties, [FeFe]-and [NiFe]-hydrogenases are phylogenetically not related.[FeFe]-hydrogenases are found in bacteria and eucarya, whereas [NiFe]-hydrogenases are found in bacteria and archaea. For recent reviews on these two types of hydrogenases, see Frey (9), Zhou et al.

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Studies on the catalytic mechanism of H2-forming methylenetetrahydromethanopterin dehydrogenase: para-ortho H2 conversion rates in H2O and D2O

Cited by 34 publications

References 0 publications

Carbon and hydrogen isotope fractionation by moderately thermophilic methanogens 1 1Associate editor: N. E. Ostrom

Carbon and hydrogen isotope fractionation by moderately thermophilic methanogens 1 1Associate editor: N. E. Ostrom

A Glutamate Is the Essential Proton Transfer Gate during the Catalytic Cycle of the [NiFe] Hydrogenase

The Iron-Sulfur Cluster-free Hydrogenase (Hmd) Is a Metalloenzyme with a Novel Iron Binding Motif

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