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Fraser A Armstrong - One of the best experts on this subject based on the ideXlab platform.
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catalytic electron transport in chromatium vinosum nife Hydrogenase application of voltammetry in detecting redox active centers and establishing that hydrogen oxidation is very fast even at potentials close to the reversible h h2 value
Biochemistry, 1999Co-Authors: Harsh R Pershad, Jillian L C Duff, Hendrik A Heering, Evert C Duin, Simon P J Albracht, Fraser A ArmstrongAbstract:The nickel−Iron Hydrogenase from Chromatium vinosum adsorbs at a pyrolytic graphite edge-plane (PGE) electrode and catalyzes rapid interconversion of H+(aq) and H2 at potentials expected for the half-cell reaction 2H+ ⇄ H2, i.e., without the need for overpotentials. The voltammetry mirrors characteristics determined by conventional methods, while affording the capabilities for exquisite control and measurement of potential-dependent activities and substrate−product mass transport. Oxidation of H2 is extremely rapid; at 10% partial pressure H2, mass transport control persists even at the highest electrode rotation rates. The turnover number for H2 oxidation lies in the range of 1500−9000 s-1 at 30 °C (pH 5−8), which is significantly higher than that observed using methylene blue as the electron acceptor. By contrast, proton reduction is slower and controlled by processes occurring in the enzyme. Carbon monoxide, which binds reversibly to the NiFe site in the active form, inhibits electrocatalysis and allow...
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catalytic electron transport in chromatium vinosum nife Hydrogenase application of voltammetry in detecting redox active centers and establishing that hydrogen oxidation is very fast even at potentials close to the reversible h h2 value
Biochemistry, 1999Co-Authors: Harsh R Pershad, Jillian L C Duff, Hendrik A Heering, Evert C Duin, Simon P J Albracht, Fraser A ArmstrongAbstract:The nickel−Iron Hydrogenase from Chromatium vinosum adsorbs at a pyrolytic graphite edge-plane (PGE) electrode and catalyzes rapid interconversion of H+(aq) and H2 at potentials expected for the half-cell reaction 2H+ ⇄ H2, i.e., without the need for overpotentials. The voltammetry mirrors characteristics determined by conventional methods, while affording the capabilities for exquisite control and measurement of potential-dependent activities and substrate−product mass transport. Oxidation of H2 is extremely rapid; at 10% partial pressure H2, mass transport control persists even at the highest electrode rotation rates. The turnover number for H2 oxidation lies in the range of 1500−9000 s-1 at 30 °C (pH 5−8), which is significantly higher than that observed using methylene blue as the electron acceptor. By contrast, proton reduction is slower and controlled by processes occurring in the enzyme. Carbon monoxide, which binds reversibly to the NiFe site in the active form, inhibits electrocatalysis and allow...
Björn Åkermark - One of the best experts on this subject based on the ideXlab platform.
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noncovalent assembly of a metalloporphyrin and an Iron Hydrogenase active site model photo induced electron transfer and hydrogen generation
Journal of Physical Chemistry B, 2008Co-Authors: Xueqiang Li, Mei Wang, Suping Zhang, Yong Na, Björn ÅkermarkAbstract:A noncovalent assembly of a pyridyl-functionalized Hydrogenase active-site model complex and zinc tetraphenylporphyrin has been obtained and characterized. Upon light irradiation, fluorescence quenching by electron transfer was observed from the singlet excited state of the porphyrin to the diIron center, and the mechanism was verified by fluorescence lifetime and transient absorption spectroscopic measurements. In contrast to molecular dyads linked by covalent bonds, the assembled system was designed to avoid charge recombination via complex dissociation after photo-induced electron transfer. Visible light-driven hydrogen generation was observed from this self-assembled system. The assembling strategy employed in this study has the potential to be used for any other Hydrogenase models in the future.
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Iron Hydrogenase active site mimics in supramolecular systems aiming for light driven hydrogen production
Coordination Chemistry Reviews, 2005Co-Authors: Licheng Sun, Björn Åkermark, Sascha OttAbstract:Models of the Iron Hydrogenase active site [(μ-DT)Fe2(CO)6] (DT: dithiolate) have been synthesized where the dithiolate co-factor bears a functional group to allow for their incorporation into supramolecular systems. Covalently linked to ruthenium(II) polypyridyl photosensitizers, the resulting ruthenium–diIron complexes represent the first members of a new class of dyads designed to promote the light-driven production of hydrogen. The functionalized diIron complexes have been characterized by X-ray crystallography. The redox properties of all complexes were investigated by cyclic voltammetry and the interactions between the photo-excited ruthenium moiety and the diIron unit in these dyads were evaluated by time-resolved spectroscopy.
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influence of tertiary phosphanes on the coordination configurations and electrochemical properties of Iron Hydrogenase model complexes crystal structures of μ s2c3h6 fe2 co 6 nln l pme2ph n 1 2 pph3 p oet 3 n 1
European Journal of Inorganic Chemistry, 2005Co-Authors: Ping Li, Chengjiang He, Changneng Chen, Guanghua Li, Mei Wang, Björn ÅkermarkAbstract:A series of mono- and disubstituted diIron complexes [(μ-pdt)Fe2(CO)5L] [pdt = 1,3-propanedithiolato; L = PMe3 (2), PMe2Ph (3PPh3 (4), P(OEt)3 (5)] and [(μ-pdt)Fe2(CO)4L2] [L = PMe2Ph (6), PPh3 (7), P(OEt)3 (8)] were prepared as Fe-only Hydrogenase-active-site models by controllable CO displacement of [(μ-pdt)Fe2(CO)6] by tertiary phosphanes. The coordination configurations of 3–6 were characterized by X-ray crystallography. Disubstituted diIron complex 6 features an apical/apical coordination mode, instead of the typical transoid basal/basal configuration. The electrochemistry of 2–6 and 8 was studied by cyclic voltammetry to evaluate the effects of different tertiary phosphane ligands on the redox properties of the Iron atoms of model complexes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
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a biomimetic pathway for hydrogen evolution from a model of the Iron Hydrogenase active site
Angewandte Chemie, 2004Co-Authors: Sascha Ott, Björn Åkermark, Mikael Kritikos, Licheng Sun, Reiner LomothAbstract:A Biomimetic Pathway for Hydrogen Evolution from a Model of the Iron Hydrogenase Active Site
Marcetta Y. Darensbourg - One of the best experts on this subject based on the ideXlab platform.
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cyanide bridged Iron complexes as biomimetics of tri Iron arrangements in maturases of the h cluster of the di Iron Hydrogenase
Chemical Science, 2016Co-Authors: Allen M Lunsford, Michael B. Hall, Christopher C Beto, Shengda Ding, Ozlen F Erdem, Ning Wang, Nattamai Bhuvanesh, Marcetta Y. DarensbourgAbstract:Developing from certain catalytic processes required for ancient life forms, the H2 processing enzymes [NiFe]- and [FeFe]-Hydrogenase (H2ase) have active sites that are organometallic in composition, possessing carbon monoxide and cyanide as ligands. Simple synthetic analogues of the 2Fe portion of the active site of [FeFe]-H2ase have been shown to dock into the empty carrier (maturation) protein, apo-Hyd-F, via the bridging ability of a terminal cyanide ligand from a low valent FeIFeI unit to the Iron of a 4Fe4S cluster of Hyd-F, with spectral evidence indicating CN isomerization during the coupling process (Berggren, et al., Nature, 2013, 499, 66–70). To probe the requirements for such cyanide couplings, we have prepared and characterized four cyanide-bridged analogues of 3-Fe systems with features related to the organoIron moiety within the loaded HydF protein. As in classical organometallic chemistry, the orientation of the CN bridge in the biomimetics is determined by the precursor reagents; no cyanide flipping or linkage isomerization was observed. Density functional theory computations evaluated the energetics of cyanide isomerization in such [FeFe]–CN–Fe ⇌ [FeFe]–NC–Fe units, and found excessively high barriers account for the failure to observe the alternative isomers. These results highlight roles for cyanide as an unusual ligand in biology that may stabilize low spin Iron in [FeFe]-Hydrogenase, and can act as a bridge connecting multi-Iron units during bioassembly of the active site.
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mechanism of electrocatalytic hydrogen production by a di Iron model of Iron Iron Hydrogenase a density functional theory study of proton dissociation constants and electrode reduction potentials
Dalton Transactions, 2010Co-Authors: Panida Surawatanawong, Marcetta Y. Darensbourg, Michael B. HallAbstract:Simple dinuclear Iron dithiolates such as (μ-SCH2CH2CH2S)[Fe(CO)3]2, (1) and (μ-SCH2CH2S)[Fe(CO)3]2 (2) are functional models for diIron-Hydrogenases, [FeFe]-H2ases, that catalyze the reduction of protons to H2. The mechanism of H2 production with 2 as the catalyst and with both toluenesulfonic (HOTs) and acetic (HOAc) acids as the H+ source in CH3CN solvent has been examined by density functional theory (DFT). Proton dissociation constants (pKa) and electrode reduction potentials (E°) are directly computed and compared to the measured pKa of HOTs and HOAc acids and the experimental reduction potentials. Computations show that when the strong acid, HOTs, is used as a proton source the one-electron reduced species 2− can be protonated to form a bridging hydride complex as the most stable structure. Then, this species can be reduced and protonated to form dihydrogen and regenerate 2. This cycle produces H2via an ECEC process at an applied potential of −1.8 V vs. Fc/Fc+. A second faster process opens for this system when the species produced at the ECEC step above is further reduced and H2 release returns the system to 2− rather than 2, an E[CECE] process. On the other hand, when the weak acid, HOAc, is the proton source a more negative applied reduction potential (−2.2 V vs. Fc/Fc+) is necessary. At this potential two one-electron reductions yield the dianion 22− before the first protonation, which in this case occurs on the thiolate. Subsequent reduction and protonation form dihydrogen and regenerate 2− through an E[ECEC] process.
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de novo design of synthetic di Iron i complexes as structural models of the reduced form of Iron Iron Hydrogenase
Inorganic Chemistry, 2006Co-Authors: Marcetta Y. Darensbourg, Michael B. HallAbstract:Simple synthetic di-Iron dithiolate complexes provide good models of the composition of the active site of the Iron−Iron Hydrogenase enzymes. However, the formally FeIFeI complexes synthesized to date fail to reproduce the precise orientation of the diatomic ligands about the Iron centers that is observed in the molecular structure of the reduced form of the enzyme active site. This structural difference is often used to explain the fact that the synthetic di-Iron complexes are generally poor catalysts when compared to the enzyme. Herein, density functional theory computations are used for the rational design of synthetic complexes as structural models of the reduced form of the enzyme active site. These computations suggest several possible synthetic targets. The synthesis of complexes containing five-atom S-to-S linkers of the form S(CH2)2X(CH2)2S (X = CH2, NH, or O) or pendant functionalities attached to the three-carbon framework is one method. Another approach is the synthesis of asymmetrically subst...
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the hydrophilic phosphatriazaadamantane ligand in the development of h2 production electrocatalysts Iron Hydrogenase model complexes
Journal of the American Chemical Society, 2004Co-Authors: Rosario Mejiarodriguez, Daesung Chong, Manuel P Soriaga, Joseph H Reibenspies, Marcetta Y. DarensbourgAbstract:As functional biomimics of the hydrogen-producing capability of the dinuclear active site in [Fe]H2ase, the FeIFeI organometallic complexes, (μ-pdt)[Fe(CO)2PTA]2, 1-PTA2, (pdt = SCH2CH2CH2S; PTA = 1,3,5-triaza-7-phosphaadamantane), and (μ-pdt)[Fe(CO)3][Fe(CO)2PTA], 1-PTA, were synthesized and fully characterized. For comparison to the hydrophobic (μ-pdt)[Fe(CO)2(PMe3)]2 and {(μ-H)(μ-pdt)[Fe(CO)2(PMe3)]2}+ analogues, electrochemical responses of 1-PTA2 and 1-(PTA·H+)2 were recorded in acetonitrile and in acetonitrile/water mixtures in the absence and presence of acetic acid. The production of H2 and the dependence of current on acid concentration indicated that the complexes were solution electrocatalysts that decreased over-voltage for H+ reduction from HOAc in CH3CN by up to 600 mV. The most effective electrocatalyst is the asymmetric 1-PTA species, which promotes H2 formation from HOAc (pKa in CH3CN = 22.6) at −1.4 V in CH3CN/H2O mixtures at the Fe0FeI redox level. Functionalization of the PTA ligand vi...
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electrocatalysis of hydrogen production by active site analogues of the Iron Hydrogenase enzyme structure function relationships
Dalton Transactions, 2003Co-Authors: Daesung Chong, Irene P Georgakaki, Rosario Mejiarodriguez, Jean Sanabriachinchilla, Manuel P Soriaga, Marcetta Y. DarensbourgAbstract:A series of binuclear FeIFeI complexes, (μ-SEt)2[Fe(CO)2L]2 (L = CO (1), PMe3 (1-P)), (μ-SRS)[Fe(CO)2L]2 (R = CH2CH2 (μ-edt): L = CO (2), PMe3 (2-P); R = CH2CH2CH2(μ-pdt): L = CO (3), PMe3 (3-P); and R = o-CH2C6H4CH2 (μ-o-xyldt): L = CO (4), PMe3 (4-P)), that serve as structural models for the active site of Fe-Hydrogenase are shown to be electrocatalysts for H2 production in the presence of acetic acid in acetonitrile. The redox levels for H2 production were established by spectroelectrochemistry to be Fe0Fe0 for the all-CO complexes and FeIFe0 for the PMe3-substituted derivatives. As electrocatalysts, the PMe3 derivatives are more stable and more sensitive to acid concentration than the all-CO complexes. The electrocatalysis is initiated by electrochemical reduction of these diIron complexes, which subsequently, under weak acid conditions, undergo protonation of the reduced Iron center to produce H2. An (η2-H2)FeII–Fe0/I intermediate is suggested and probable electrochemical mechanisms are discussed.
Roussel Michaël - One of the best experts on this subject based on the ideXlab platform.
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Séquençage du génome du parasite intestinal Blastocystis sp. (ST7) : vers une meilleure compréhension des capacités métaboliques d'organites apparentés aux mitochondries chez ce microorganisme anaérobie
HAL CCSD, 2011Co-Authors: Roussel MichaëlAbstract:Blastocystis sp. is a highly prevalent anaerobic eukaryotic stramenopile parasite found in the intestinal tract of humans and various animals. This microorganism, sometimes associated with acute intestinal disorders, could be responsible for functional intestinal disorders such as the irritable bowel syndrom (IBS). As part of a collaborative sequencing project with the Genoscope (CEA Evry, France), we were able to caracterize the smallest stramenopile genome sequenced to date (18.8 Mbp) with a 6020 genes coding capacity. The gain of many genes through horizontal gene transfer is amajor characteristic of this genome, which shows extensive genomic rearrangements. Despite the anaerobic nature of Blastocytists sp., this eukaryote harbours nevertheless mitochondrion-like organelles (MLOs). We have shown that these organelles have a 29.27 kbp mitochondrial-type circular genome that lacks cytochrome coding genes. In silico analysis allowed us to predict the MLOs proteome (365 proteins), with the subsequent predictive model of the metabolic pathways associated with these organelles, including an electron transport chain (ETC) restricted to complex I and II. We have shown that MLOs shared common characteristics with anaerobic mitochondrion and hydrogenosomes (presence of a PFOR and an Iron-Hydrogenase), which could mean that Blastocystis sp. harbours modified anaerobic mitochondrion that resulted from the parasite adaptation to its anaerobic envIronment. In addition, Blastocytis sp. secretome prediction reveals the presence of potential virulence factors, which could be involved in the degradation of the intestinal epithelium as well as the host immune system bypass.Blastocystis sp., est un straménopile parasite anaérobie fréquemment rencontré dans le tractus gastro-intestinal de l’homme et de divers animaux. Ce microorganisme, parfois responsable de désordres digestifs aigus, pourrait conduire à des troubles fonctionnels intestinaux tels que le syndrome de l’intestin irritable (IBS). Le génome de Blastocystis sp., qui a fait l'objet d'un projet de séquençage en collaboration avec le Génoscope d’Evry, nous a permis de caractériser le plus petit génome de straménopile séquencé à ce jour (18,8 Mpb), avec une capacité codante de 6020 gènes. L’acquisition de nombreux gènes par transferts horizontaux est une caractéristique majeure de ce génome, qui montre d’abondants réarrangements génomiques. Bien qu’évoluant en anaérobiose, Blastocystis sp. possède des organites morphologiquement proches des mitochondries, appelés mitochondrion-like organelles (MLOs). Nous avons montré que ces organites comportaient un génome circulaire de type mitochondrial de 29,27 kpb, mais dépourvu des gènes codant pour les cytochromes. Des analyses in silico nous ont permis de caractériser le protéome des MLOs (365 protéines), conduisant à l’établissement d’un modèle prédictif des voies métaboliques associées à ces organites, avec notamment une chaine respiratoire limitée aux complexes I et II. Nous avons ainsi montré que les MLOs présentent des caractères communs aux mitochondries anaérobies et aux hydrogénosomes (présence d’une PFOR et d’une hydrogénase à fer), suggérant que Blastocystis sp. comporte des mitochondries anaérobies modifiées, qui résulteraient d’une adaptation du parasite à son envIronnement. Par ailleurs, la prédiction du sécrétome de Blastocystis sp. révèle la présence de facteurs de virulence potentiels, pouvant être impliqués dans l’altération de l’épithélium intestinal et le contournement du système immunitaire de l’hôte
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Genome sequencing of the intestinal parasite Blastocystis sp. (ST7) : towards a better understanding of the metabolic capacities of mitochondria-related organelles in this anaerobic microorganism
2011Co-Authors: Roussel MichaëlAbstract:Blastocystis sp., est un straménopile parasite anaérobie fréquemment rencontré dans le tractus gastro-intestinal de l’homme et de divers animaux. Ce microorganisme, parfois responsable de désordres digestifs aigus, pourrait conduire à des troubles fonctionnels intestinaux tels que le syndrome de l’intestin irritable (IBS). Le génome de Blastocystis sp., qui a fait l'objet d'un projet de séquençage en collaboration avec le Génoscope d’Evry, nous a permis de caractériser le plus petit génome de straménopile séquencé à ce jour (18,8 Mpb), avec une capacité codante de 6020 gènes. L’acquisition de nombreux gènes par transferts horizontaux est une caractéristique majeure de ce génome, qui montre d’abondants réarrangements génomiques. Bien qu’évoluant en anaérobiose, Blastocystis sp. possède des organites morphologiquement proches des mitochondries, appelés mitochondrion-like organelles (MLOs). Nous avons montré que ces organites comportaient un génome circulaire de type mitochondrial de 29,27 kpb, mais dépourvu des gènes codant pour les cytochromes. Des analyses in silico nous ont permis de caractériser le protéome des MLOs (365 protéines), conduisant à l’établissement d’un modèle prédictif des voies métaboliques associées à ces organites, avec notamment une chaine respiratoire limitée aux complexes I et II. Nous avons ainsi montré que les MLOs présentent des caractères communs aux mitochondries anaérobies et aux hydrogénosomes (présence d’une PFOR et d’une hydrogénase à fer), suggérant que Blastocystis sp. comporte des mitochondries anaérobies modifiées, qui résulteraient d’une adaptation du parasite à son envIronnement. Par ailleurs, la prédiction du sécrétome de Blastocystis sp. révèle la présence de facteurs de virulence potentiels, pouvant être impliqués dans l’altération de l’épithélium intestinal et le contournement du système immunitaire de l’hôte.Blastocystis sp. is a highly prevalent anaerobic eukaryotic stramenopile parasite found in the intestinal tract of humans and various animals. This microorganism, sometimes associated with acute intestinal disorders, could be responsible for functional intestinal disorders such as the irritable bowel syndrom (IBS). As part of a collaborative sequencing project with the Genoscope (CEA Evry, France), we were able to caracterize the smallest stramenopile genome sequenced to date (18.8 Mbp) with a 6020 genes coding capacity. The gain of many genes through horizontal gene transfer is amajor characteristic of this genome, which shows extensive genomic rearrangements. Despite the anaerobic nature of Blastocytists sp., this eukaryote harbours nevertheless mitochondrion-like organelles (MLOs). We have shown that these organelles have a 29.27 kbp mitochondrial-type circular genome that lacks cytochrome coding genes. In silico analysis allowed us to predict the MLOs proteome (365 proteins), with the subsequent predictive model of the metabolic pathways associated with these organelles, including an electron transport chain (ETC) restricted to complex I and II. We have shown that MLOs shared common characteristics with anaerobic mitochondrion and hydrogenosomes (presence of a PFOR and an Iron-Hydrogenase), which could mean that Blastocystis sp. harbours modified anaerobic mitochondrion that resulted from the parasite adaptation to its anaerobic envIronment. In addition, Blastocytis sp. secretome prediction reveals the presence of potential virulence factors, which could be involved in the degradation of the intestinal epithelium as well as the host immune system bypass
Harsh R Pershad - One of the best experts on this subject based on the ideXlab platform.
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catalytic electron transport in chromatium vinosum nife Hydrogenase application of voltammetry in detecting redox active centers and establishing that hydrogen oxidation is very fast even at potentials close to the reversible h h2 value
Biochemistry, 1999Co-Authors: Harsh R Pershad, Jillian L C Duff, Hendrik A Heering, Evert C Duin, Simon P J Albracht, Fraser A ArmstrongAbstract:The nickel−Iron Hydrogenase from Chromatium vinosum adsorbs at a pyrolytic graphite edge-plane (PGE) electrode and catalyzes rapid interconversion of H+(aq) and H2 at potentials expected for the half-cell reaction 2H+ ⇄ H2, i.e., without the need for overpotentials. The voltammetry mirrors characteristics determined by conventional methods, while affording the capabilities for exquisite control and measurement of potential-dependent activities and substrate−product mass transport. Oxidation of H2 is extremely rapid; at 10% partial pressure H2, mass transport control persists even at the highest electrode rotation rates. The turnover number for H2 oxidation lies in the range of 1500−9000 s-1 at 30 °C (pH 5−8), which is significantly higher than that observed using methylene blue as the electron acceptor. By contrast, proton reduction is slower and controlled by processes occurring in the enzyme. Carbon monoxide, which binds reversibly to the NiFe site in the active form, inhibits electrocatalysis and allow...
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catalytic electron transport in chromatium vinosum nife Hydrogenase application of voltammetry in detecting redox active centers and establishing that hydrogen oxidation is very fast even at potentials close to the reversible h h2 value
Biochemistry, 1999Co-Authors: Harsh R Pershad, Jillian L C Duff, Hendrik A Heering, Evert C Duin, Simon P J Albracht, Fraser A ArmstrongAbstract:The nickel−Iron Hydrogenase from Chromatium vinosum adsorbs at a pyrolytic graphite edge-plane (PGE) electrode and catalyzes rapid interconversion of H+(aq) and H2 at potentials expected for the half-cell reaction 2H+ ⇄ H2, i.e., without the need for overpotentials. The voltammetry mirrors characteristics determined by conventional methods, while affording the capabilities for exquisite control and measurement of potential-dependent activities and substrate−product mass transport. Oxidation of H2 is extremely rapid; at 10% partial pressure H2, mass transport control persists even at the highest electrode rotation rates. The turnover number for H2 oxidation lies in the range of 1500−9000 s-1 at 30 °C (pH 5−8), which is significantly higher than that observed using methylene blue as the electron acceptor. By contrast, proton reduction is slower and controlled by processes occurring in the enzyme. Carbon monoxide, which binds reversibly to the NiFe site in the active form, inhibits electrocatalysis and allow...
