1
|
Rao G, Yu X, Zhang Y, Rauchfuss TB, Britt RD. Fully Refined Semisynthesis of the [FeFe] Hydrogenase H-Cluster. Biochemistry 2023; 62:2868-2877. [PMID: 37691492 DOI: 10.1021/acs.biochem.3c00393] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/12/2023]
Abstract
[FeFe] hydrogenases contain a 6-Fe cofactor that serves as the active site for efficient redox interconversion between H2 and protons. The biosynthesis of the so-called H-cluster involves unusual enzymatic reactions that synthesize organometallic Fe complexes containing azadithiolate, CO, and CN- ligands. We have previously demonstrated that specific synthetic [Fe(CO)x(CN)y] complexes can be used to functionally replace proposed Fe intermediates in the maturation reaction. Here, we report the results from performing such cluster semisynthesis in the context of a recent fully defined cluster maturation procedure, which eliminates unknown components previously employed from Escherichia coli cell lysate and demonstrate this provides a concise route to H-cluster synthesis. We show that formaldehyde can be used as a simple reagent as the carbon source of the bridging adt ligand of H-cluster in lieu of serine/serine hydroxymethyltransferase. In addition to the actual H-cluster, we observe the formation of several H-cluster-like species, the identities of which are probed by cryogenic photolysis combined with EPR/ENDOR spectroscopy.
Collapse
Affiliation(s)
- Guodong Rao
- Department of Chemistry, University of California, Davis, Davis, California 95616, United States
| | - Xin Yu
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61820, United States
| | - Yu Zhang
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61820, United States
| | - Thomas B Rauchfuss
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61820, United States
| | - R David Britt
- Department of Chemistry, University of California, Davis, Davis, California 95616, United States
- Miller Institute for Basic Research in Science, University of California, Berkeley, Berkeley, California 94720, United States
| |
Collapse
|
2
|
Sensi M, Baffert C, Fradale L, Gauquelin C, Soucaille P, Meynial-Salles I, Bottin H, de Gioia L, Bruschi M, Fourmond V, Léger C, Bertini L. Photoinhibition of FeFe Hydrogenase. ACS Catal 2017. [DOI: 10.1021/acscatal.7b02252] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Affiliation(s)
- Matteo Sensi
- Aix Marseille University, CNRS, BIP UMR 7281, 13402 CEDEX 20 Marseille, France
- Department
of Biotechnologies and Biosciences, University of Milano-Bicocca, Piazza
della Scienza 2, 20126 Milan, Italy
| | - Carole Baffert
- Aix Marseille University, CNRS, BIP UMR 7281, 13402 CEDEX 20 Marseille, France
| | - Laura Fradale
- Aix Marseille University, CNRS, BIP UMR 7281, 13402 CEDEX 20 Marseille, France
| | - Charles Gauquelin
- Université de Toulouse, INSA, UPS, INP, LISBP, INRA:UMR792,135
CNRS:UMR 5504, Avenue
de Rangueil, 31077 Toulouse, France
| | - Philippe Soucaille
- Université de Toulouse, INSA, UPS, INP, LISBP, INRA:UMR792,135
CNRS:UMR 5504, Avenue
de Rangueil, 31077 Toulouse, France
| | - Isabelle Meynial-Salles
- Université de Toulouse, INSA, UPS, INP, LISBP, INRA:UMR792,135
CNRS:UMR 5504, Avenue
de Rangueil, 31077 Toulouse, France
| | - Hervé Bottin
- Institut
de Biologie Intégrative de la Cellule (I2BC), Institut Frédéric
Joliot, CEA, CNRS, Univ Paris-Sud, Université Paris-Saclay, F-91198 CEDEX Gif-Sur-Yvette, France
| | - Luca de Gioia
- Department
of Biotechnologies and Biosciences, University of Milano-Bicocca, Piazza
della Scienza 2, 20126 Milan, Italy
| | - Maurizio Bruschi
- Department
of Earth and Environmental Sciences, Milano-Bicocca University, Piazza della
Scienza 1, 20126 Milan, Italy
- Department
of Biotechnologies and Biosciences, University of Milano-Bicocca, Piazza
della Scienza 2, 20126 Milan, Italy
| | - Vincent Fourmond
- Aix Marseille University, CNRS, BIP UMR 7281, 13402 CEDEX 20 Marseille, France
| | - Christophe Léger
- Aix Marseille University, CNRS, BIP UMR 7281, 13402 CEDEX 20 Marseille, France
| | - Luca Bertini
- Department
of Biotechnologies and Biosciences, University of Milano-Bicocca, Piazza
della Scienza 2, 20126 Milan, Italy
| |
Collapse
|
3
|
Artz JH, Mulder DW, Ratzloff MW, Lubner CE, Zadvornyy OA, LeVan AX, Williams SG, Adams MWW, Jones AK, King PW, Peters JW. Reduction Potentials of [FeFe]-Hydrogenase Accessory Iron-Sulfur Clusters Provide Insights into the Energetics of Proton Reduction Catalysis. J Am Chem Soc 2017. [PMID: 28635269 DOI: 10.1021/jacs.7b02099] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
An [FeFe]-hydrogenase from Clostridium pasteurianum, CpI, is a model system for biological H2 activation. In addition to the catalytic H-cluster, CpI contains four accessory iron-sulfur [FeS] clusters in a branched series that transfer electrons to and from the active site. In this work, potentiometric titrations have been employed in combination with electron paramagnetic resonance (EPR) spectroscopy at defined electrochemical potentials to gain insights into the role of the accessory clusters in catalysis. EPR spectra collected over a range of potentials were deconvoluted into individual components attributable to the accessory [FeS] clusters and the active site H-cluster, and reduction potentials for each cluster were determined. The data suggest a large degree of magnetic coupling between the clusters. The distal [4Fe-4S] cluster is shown to have a lower reduction potential (∼ < -450 mV) than the other clusters, and molecular docking experiments indicate that the physiological electron donor, ferredoxin (Fd), most favorably interacts with this cluster. The low reduction potential of the distal [4Fe-4S] cluster thermodynamically restricts the Fdox/Fdred ratio at which CpI can operate, consistent with the role of CpI in recycling Fdred that accumulates during fermentation. Subsequent electron transfer through the additional accessory [FeS] clusters to the H-cluster is thermodynamically favorable.
Collapse
Affiliation(s)
- Jacob H Artz
- Institute of Biological Chemistry, Washington State University , 258 Clark Hall, Pullman, Washington 99163, United States
| | - David W Mulder
- Biosciences Center, National Renewable Energy Laboratory , 15013 Denver West Parkway, Golden, Colorado 80401, United States
| | - Michael W Ratzloff
- Biosciences Center, National Renewable Energy Laboratory , 15013 Denver West Parkway, Golden, Colorado 80401, United States
| | - Carolyn E Lubner
- Biosciences Center, National Renewable Energy Laboratory , 15013 Denver West Parkway, Golden, Colorado 80401, United States
| | - Oleg A Zadvornyy
- Institute of Biological Chemistry, Washington State University , 258 Clark Hall, Pullman, Washington 99163, United States
| | - Axl X LeVan
- Department of Chemistry and Biochemistry, Montana State University , 224 Chemistry and Biochemistry Building, Bozeman, Montana 59717, United States
| | - S Garrett Williams
- School of Molecular Sciences, Arizona State University , P.O. Box 871604, Tempe, Arizona 85287, United States
| | - Michael W W Adams
- B216B Life Sciences Complex, Department of Biochemistry, The University of Georgia , Athens, Georgia 30602, United States
| | - Anne K Jones
- School of Molecular Sciences, Arizona State University , P.O. Box 871604, Tempe, Arizona 85287, United States
| | - Paul W King
- Biosciences Center, National Renewable Energy Laboratory , 15013 Denver West Parkway, Golden, Colorado 80401, United States
| | - John W Peters
- Institute of Biological Chemistry, Washington State University , 258 Clark Hall, Pullman, Washington 99163, United States
| |
Collapse
|
4
|
Hunt NT, Wright JA, Pickett C. Detection of Transient Intermediates Generated from Subsite Analogues of [FeFe] Hydrogenases. Inorg Chem 2015; 55:399-410. [DOI: 10.1021/acs.inorgchem.5b02477] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Neil T. Hunt
- Department of Physics, University of Strathclyde, SUPA, Glasgow G4 0NG, United Kingdom
| | - Joseph A. Wright
- Energy Materials Laboratory, School of
Chemistry, University of East Anglia (UEA), Norwich Research Park, Norwich NR4 7TJ, United Kingdom
| | - Christopher Pickett
- Energy Materials Laboratory, School of
Chemistry, University of East Anglia (UEA), Norwich Research Park, Norwich NR4 7TJ, United Kingdom
| |
Collapse
|
5
|
Thornley WA, Bitterwolf TE. Intramolecular CH Activation and Metallacycle Aromaticity in the Photochemistry of [FeFe]-Hydrogenase Model Compounds in Low-Temperature Frozen Matrices. Chemistry 2015; 21:18218-29. [PMID: 26541102 DOI: 10.1002/chem.201503826] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2015] [Indexed: 11/11/2022]
Affiliation(s)
- Wyatt A Thornley
- Department of Chemistry, University of Idaho, 875 Perimeter Dr., Moscow, ID 83844 (USA).
| | - Thomas E Bitterwolf
- Department of Chemistry, University of Idaho, 875 Perimeter Dr., Moscow, ID 83844 (USA).
| |
Collapse
|
6
|
Bertini L, Greco C, Bruschi M, Fantucci P, De Gioia L. CO Affinity and Bonding Properties of [FeFe] Hydrogenase Active Site Models. A DFT Study. Organometallics 2010. [DOI: 10.1021/om900658b] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Luca Bertini
- Department of Biotechnology and Biosciences, Università degli Studi di Milano-Bicocca, Piazza della Scienza, 2, 20126 Milan, Italy
| | - Claudio Greco
- Department of Biotechnology and Biosciences, Università degli Studi di Milano-Bicocca, Piazza della Scienza, 2, 20126 Milan, Italy
| | - Maurizio Bruschi
- Department of Environmental Sciences, Università degli Studi di Milano-Bicocca, Piazza della Scienza, 1, 20126 Milan, Italy
| | - Piercarlo Fantucci
- Department of Biotechnology and Biosciences, Università degli Studi di Milano-Bicocca, Piazza della Scienza, 2, 20126 Milan, Italy
| | - Luca De Gioia
- Department of Biotechnology and Biosciences, Università degli Studi di Milano-Bicocca, Piazza della Scienza, 2, 20126 Milan, Italy
| |
Collapse
|
7
|
Peters JW. Carbon Monoxide and Cyanide Ligands in the Active Site of [FeFe]-Hydrogenases. METAL-CARBON BONDS IN ENZYMES AND COFACTORS 2009. [DOI: 10.1039/9781847559333-00179] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The [FeFe]-hydrogenases, although share common features when compared to other metal containing hydrogenases, clearly have independent evolutionary origins. Examples of [FeFe]-hydrogenases have been characterized in detail by biochemical and spectroscopic approaches and the high resolution structures of two examples have been determined. The active site H-cluster is a complex bridged metal assembly in which a [4Fe-4S] cubane is bridged to a 2Fe subcluster with unique non-protein ligands including carbon monoxide, cyanide, and a five carbon dithiolate. Carbon monoxide and cyanide ligands as a component of a native active metal center is a property unique to the metal containing hydrogenases and there has been considerable attention to the characterization of the H-cluster at the level of electronic structure and mechanism as well as to defining the biological means to synthesize such a unique metal cluster. The chapter describes the structural architecture of [FeFe]-hydrogenases and key spectroscopic observations that have afforded the field with a fundamental basis for understanding the relationship between structure and reactivity of the H-cluster. In addition, the results and ideas concerning the topic of H-cluster biosynthesis as an emerging and fascinating area of research, effectively reinforcing the potential linkage between iron-sulfur biochemistry to the role of iron-sulfur minerals in prebiotic chemistry and the origin of life.
Collapse
Affiliation(s)
- John W. Peters
- Montana State University, Department of Chemistry and Biochemistry and the Astrobiology Biogeocatalysis Research Center Bozeman, MT 59717 USA
| |
Collapse
|
8
|
Thomas CM, Liu T, Hall MB, Darensbourg MY. Series of Mixed Valent Fe(II)Fe(I) Complexes That Model the Hox State of [FeFe]Hydrogenase: Redox Properties, Density-Functional Theory Investigation, and Reactivities with Extrinsic CO. Inorg Chem 2008; 47:7009-24. [DOI: 10.1021/ic800654a] [Citation(s) in RCA: 105] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
| | - Tianbiao Liu
- Department of Chemistry, Texas A&M University, College Station, Texas 77845
| | - Michael B. Hall
- Department of Chemistry, Texas A&M University, College Station, Texas 77845
| | | |
Collapse
|
9
|
Deletion of iscR stimulates recombinant clostridial Fe–Fe hydrogenase activity and H2-accumulation in Escherichia coli BL21(DE3). Appl Microbiol Biotechnol 2008; 78:853-62. [DOI: 10.1007/s00253-008-1377-6] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2007] [Revised: 01/17/2008] [Accepted: 01/17/2008] [Indexed: 10/22/2022]
|
10
|
Blackburn JL, Svedruzic D, McDonald TJ, Kim YH, King PW, Heben MJ. Raman spectroscopy of charge transfer interactions between single wall carbon nanotubes and [FeFe] hydrogenase. Dalton Trans 2008:5454-61. [DOI: 10.1039/b806379f] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
|
11
|
Lubitz W, Reijerse E, van Gastel M. [NiFe] and [FeFe] Hydrogenases Studied by Advanced Magnetic Resonance Techniques. Chem Rev 2007; 107:4331-65. [PMID: 17845059 DOI: 10.1021/cr050186q] [Citation(s) in RCA: 376] [Impact Index Per Article: 22.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Wolfgang Lubitz
- Max-Planck-Institut für Bioanorganische Chemie, Stiftstrasse 34-36, D-45470 Mülheim an der Ruhr, Germany
| | | | | |
Collapse
|
12
|
Silakov A, Reijerse EJ, Albracht SPJ, Hatchikian EC, Lubitz W. The Electronic Structure of the H-Cluster in the [FeFe]-Hydrogenase from Desulfovibrio desulfuricans: A Q-band 57Fe-ENDOR and HYSCORE Study. J Am Chem Soc 2007; 129:11447-58. [PMID: 17722921 DOI: 10.1021/ja072592s] [Citation(s) in RCA: 140] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The active site of the (57)Fe-enriched [FeFe]-hydrogenase (i.e., the "H-cluster") from Desulfovibrio desulfuricans has been examined using advanced pulse EPR methods at X- and Q-band frequencies. For both the active oxidized state (H(ox)) and the CO inhibited form (H(ox)-CO) all six (57)Fe hyperfine couplings were detected. The analysis shows that the apparent spin density extends over the whole H-cluster. The investigations revealed different hyperfine couplings of all six (57)Fe nuclei in the H-cluster of the H(ox)-CO state. Four large 57Fe hyperfine couplings in the range 20-40 MHz were found (using pulse ENDOR and TRIPLE methods) and were assigned to the [4Fe-4S](H) (cubane) subcluster. Two weak (57)Fe hyperfine couplings below 5 MHz were identified using Q-band HYSCORE spectroscopy and were assigned to the [2Fe](H) subcluster. For the H(ox) state only two different 57Fe hyperfine couplings in the range 10-13 MHz were detected using pulse ENDOR. An (57)Fe line broadening analysis of the X-band CW EPR spectrum indicated, however, that all six (57)Fe nuclei in the H-cluster are contributing to the hyperfine pattern. It is concluded that in both states the binuclear subcluster [2Fe](H) assumes a [Fe(I)Fe(II)] redox configuration where the paramagnetic Fe(I) atom is attached to the [4Fe-4S](H) subcluster. The (57)Fe hyperfine interactions of the formally diamagnetic [4Fe-4S](H) are due to an exchange interaction between the two subclusters as has been discussed earlier by Popescu and Münck [Popescu, C.V.; Münck, E., J. Am. Chem. Soc. 1999, 121, 7877-7884]. This exchange coupling is strongly enhanced by binding of the extrinsic CO ligand. Binding of the dihydrogen substrate may induce a similar effect, and it is therefore proposed that the observed modulation of the electronic structure by the changing ligand surrounding plays an important role in the catalytic mechanism of [FeFe]-hydrogenase.
Collapse
Affiliation(s)
- Alexey Silakov
- Max-Planck-Institut für Bioanorganische Chemie, Stiftstrasse 34-36, Mülheim a. d. Ruhr, 45470, Germany
| | | | | | | | | |
Collapse
|
13
|
Roseboom W, De Lacey AL, Fernandez VM, Hatchikian EC, Albracht SPJ. The active site of the [FeFe]-hydrogenase from Desulfovibrio desulfuricans. II. Redox properties, light sensitivity and CO-ligand exchange as observed by infrared spectroscopy. J Biol Inorg Chem 2005; 11:102-18. [PMID: 16323019 DOI: 10.1007/s00775-005-0040-2] [Citation(s) in RCA: 180] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2005] [Accepted: 09/26/2005] [Indexed: 10/25/2022]
Abstract
In [FeFe]-hydrogenases, the H cluster (hydrogen-activating cluster) contains a di-iron centre ([2Fe]H subcluster, a (L)(CO)(CN)Fe(mu-RS2)(mu-CO)Fe(CysS)(CO)(CN) group) covalently attached to a cubane iron-sulphur cluster ([4Fe-4S]H subcluster). The Cys-thiol functions as the link between one iron (called Fe1) of the [2Fe]H subcluster and one iron of the cubane subcluster. The other iron in the [2Fe]H subcluster is called Fe2. The light sensitivity of the Desulfovibrio desulfuricans enzyme in a variety of states has been studied with infrared (IR) spectroscopy. The aerobic inactive enzyme (H(inact) state) and the CO-inhibited active form (H(ox)-CO state) were stable in light. Illumination of the H(ox) state led to a kind of cannibalization; in some enzyme molecules the H cluster was destroyed and the released CO was captured by the H clusters in other molecules to form the light-stable H(ox)-CO state. Illumination of active enzyme under 13CO resulted in the complete exchange of the two intrinsic COs bound to Fe2. At cryogenic temperatures, light induced the photodissociation of the extrinsic CO and the bridging CO of the enzyme in the H(ox)-CO state. Electrochemical redox titrations showed that the enzyme in the H(inact) state converts to the transition state (H(trans)) in a reversible one-electron redox step (E (m, pH 7) = -75 mV). IR spectra demonstrate that the added redox equivalent not only affects the [4Fe-4S]H subcluster, but also the di-iron centre. Enzyme in the H(trans) state reacts with extrinsic CO, which binds to Fe2. The H(trans) state converts irreversibly into the H(ox) state in a redox-dependent reaction most likely involving two electrons (E (m, pH 7) = -261 mV). These electrons do not end up on any of the six Fe atoms of the H cluster; the possible destiny of the two redox equivalents is discussed. An additional reversible one-electron redox reaction leads to the H(red) state (E (m, pH 7) = -354 mV), where both Fe atoms of the [2Fe]H subcluster have the same formal oxidation state. The possible oxidation states of Fe1 and Fe2 in the various enzyme states are discussed. Low redox potentials (below -500 mV) lead to destruction of the [2Fe]H subcluster.
Collapse
Affiliation(s)
- Winfried Roseboom
- Swammerdam Institute for Life Sciences, University of Amsterdam, Nieuwe Achtergracht 166, 1018 WV Amsterdam, The Netherlands
| | | | | | | | | |
Collapse
|
14
|
Albracht SPJ, Roseboom W, Hatchikian EC. The active site of the [FeFe]-hydrogenase from Desulfovibrio desulfuricans. I. Light sensitivity and magnetic hyperfine interactions as observed by electron paramagnetic resonance. J Biol Inorg Chem 2005; 11:88-101. [PMID: 16323020 DOI: 10.1007/s00775-005-0039-8] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2005] [Accepted: 09/26/2005] [Indexed: 10/25/2022]
Abstract
The hydrogen-activating cluster (H cluster) in [FeFe]-hydrogenases consists of two moieties. The [2Fe]H subcluster is a (L)(CO)(CN)Fe(mu-RS2)(mu-CO)Fe(CysS)(CO)(CN) centre. The Cys-bound Fe is called Fe1, the other iron Fe2. The Cys-thiol forms a bridge to a [4Fe-4S] cluster, the [4Fe-4S]H subcluster. We report that electron paramagnetic resonance (EPR) spectra of the 57Fe-enriched enzyme from Desulfovibrio desulfuricans in the H(ox)-CO state are consistent with a magnetic hyperfine interaction of the unpaired spin with all six Fe atoms of the H cluster. In contrast to the inactive aerobic enzyme, the active enzyme is easily destroyed by light. The [2Fe]H subcluster in some enzyme molecules loses CO by photolysis, whereupon other molecules firmly bind the released CO to form the H(ox)-CO state giving rise to the so-called axial 2.06 EPR signal. Though not destroyed by light, the H(ox)-CO state is affected by it. As demonstrated in the accompanying paper [49] two of the intrinsic COs, both bound to Fe2, can be exchanged by extrinsic 13CO during illumination at 2 degrees C. We found that only one of the three 13COs, the one at the extrinsic position, gives an EPR-detectable isotropic superhyperfine interaction of 0.6 mT. At 30 K both the inhibiting extrinsic CO bound to Fe2 and one more CO can be photolysed. EPR spectra of the photolysed products are consistent with a 3d7 system of Fe with the formal oxidation state +1. The damaged enzyme shows a light-sensitive g = 5 signal which is ascribed to an S = 3/2 form of the [2Fe](H) subcluster. The light sensitivity of the enzyme explains the occurrence of the g = 5 signal and the axial 2.06 signal in published EPR spectra of nearly all preparations studied thus far.
Collapse
Affiliation(s)
- Simon P J Albracht
- Swammerdam Institute for Life Sciences, University of Amsterdam, Nieuwe Achtergracht 166, 1018 WV, Amsterdam, The Netherlands,
| | | | | |
Collapse
|
15
|
Fiedler AT, Brunold TC. Computational Studies of the H-Cluster of Fe-Only Hydrogenases: Geometric, Electronic, and Magnetic Properties and Their Dependence on the [Fe4S4] Cubane. Inorg Chem 2005; 44:9322-34. [PMID: 16323916 DOI: 10.1021/ic050946f] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The active sites of Fe-only hydrogenases (FeHases) feature an unusual polynuclear iron-sulfur cluster, known as the H-cluster, that consists of a [Fe4S4] cubane linked to a di-iron subunit (the [2Fe]H component) via a bridging cysteine ligand (SCys). While previous computational studies of FeHases employed H-cluster models that only included the [2Fe]H component, we have utilized density functional theory (DFT), in conjunction with the broken-symmetry (BS) approach, to explore the geometric, electronic, and magnetic properties of the entire H-cluster. These calculations have allowed us to evaluate, for the first time, the influence of the [Fe4S4] cubane on the [2Fe]H component of the H-cluster in its active (Hox) and CO-inhibited (Hox-CO) states, both of which are paramagnetic (S=1/2). Our results reveal that the presence of the cubane tunes both the position and the donor strength of the SCys ligand, which, in turn, modulates the internal geometric and electronic structures of the [2Fe]H subcluster. Importantly, the BS methodology provides an accurate description of the exchange interactions within the H-cluster, permitting insight into the electronic origin of the changes in magnetic properties observed experimentally upon conversion of Hox to Hox-CO. Specifically, while the unpaired spin density in the Hox state is localized on the distal Fe center, in the Hox-CO state, it is delocalized over the [2Fe]H component, such that the proximal Fe center acquires significant spin density (where distal and proximal refer to the positions of the Fe centers relative to the cubane). To validate our H-cluster models on the basis of experimental data, two DFT-based approaches and the semiempirical INDO/S method have been employed to compute electron paramagnetic resonance parameters for the H-cluster states. While most computations yield reasonably accurate g values and ligand hyperfine coupling constants (i.e., A values) for the Hox and Hox-CO states, they fail to reproduce the isotropic 57Fe A tensors found experimentally. Finally, extension of the computational methodology employed successfully for the Hox and Hox-CO states to the metastable Hoxphoto state, generated by irradiation of the Hox-CO state at cryogenic temperatures, has allowed us to discriminate between proposed structural models for this species.
Collapse
Affiliation(s)
- Adam T Fiedler
- Department of Chemistry, University of Wisconsin-Madison, 1101 West University Avenue, Madison, Wisconsin 53706, USA
| | | |
Collapse
|
16
|
Fiedler AT, Brunold TC. Combined spectroscopic/computational study of binuclear Fe(I)-Fe(I) complexes: implications for the fully-reduced active-site cluster of Fe-only hydrogenases. Inorg Chem 2005; 44:1794-809. [PMID: 15762706 DOI: 10.1021/ic048739n] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The Fe(I)-Fe(I) dimer complex [Fe2(pdt)(CO)4(CN)2][Et4N]2 (2), where pdt = 1,3-propane dithiolate, serves as a model of the fully reduced [2Fe]H component of the H cluster, which is the active site for catalysis in Fe-only hydrogenases (FeHases). Electronic absorption, magnetic circular dichroism (MCD), and resonance Raman (rR) spectroscopies have been employed to characterize both the ground and excited states of 2 as well as those of the related complex Fe2(pdt)(CO)6 (1). These results have been combined with density functional theory (DFT) computations to produce experimentally validated bonding descriptions of 1 and 2. It is shown that Fe(I)-S covalency is significantly reduced upon dicyano substitution (i.e., conversion of 1 --> 2), while the corresponding Fe(I)-CO/CN pi-backbonding interactions are strengthened, results that are corroborated by normal-coordinate analyses of the vibrational data. Detailed assignments of the features observed in the electronic absorption spectra of 1 and 2 have been developed on the basis of time-dependent DFT (TD-DFT) calculations, which provide remarkably accurate simulations of the experimental data. For both complexes, all bands below 32,000 cm(-1) arise from transitions involving electronic excitation within the binuclear Fe-Fe core, with the most intense feature assigned to the Fe(sigma(b)) --> Fe(sigma*) transition. Analysis of the corresponding rR excitation profiles within the framework of time-dependent Heller theory reveals that in each case the Fe-Fe bond is elongated by approximately 0.3 A in the Fe(sigma(b)) --> Fe(sigma*) excited state. Finally, building upon the insights gained from the spectroscopic/computational studies of 1 and 2, our computational methodology has been extended to the reduced enzyme active site, providing insights into the electronic structure of the [2Fe]H subcluster in the H(red) state and its relationship to catalysis.
Collapse
Affiliation(s)
- Adam T Fiedler
- University of Wisconsin-Madison, Department of Chemistry, 1101 West University Avenue, Madison, Wisconsin 53706
| | | |
Collapse
|
17
|
Abstract
In the presence of CO and under turnover conditions, Mo-nitrogenase generates three different electron paramagnetic resonance (EPR) signals. One of the signals, lo-CO, is an S=1/2 signal and occurs under low CO concentrations. The other two signals, hi-CO (S=1/2) and hi(5)-CO (S=3/2) displace the lo-CO as the CO concentration is raised above 0.05 atm. Irradiation of hi-CO with visible light at 12 K converts it into lo-CO. Using a series of color filters, the corrected action spectrum is determined and shown to contain 2-3 broad maxima in the region 350-730 nm. The conversion of lo-CO back into hi-CO is accomplished by warming the sample to 77 K for 5 min. Using this temperature cycle, the rate constant for the re-association of CO with lo-CO to form hi-CO is determined in the range 12-90 K. From these data, the activation energy for this reaction is calculated to be 3.9 kJ/mol. Identical irradiation of either lo-CO or hi(5)-CO induces no spectral change, showing that both of these states are photo-stable. The photo-stability of hi(5)-CO demonstrates that it is structurally different from hi-CO.
Collapse
Affiliation(s)
- Zofia Maskos
- Department of Chemistry, Louisiana State University, Baton Rouge, LA 70803-1804, USA
| | | |
Collapse
|
18
|
Liu ZP, Hu P. A density functional theory study on the active center of Fe-only hydrogenase: characterization and electronic structure of the redox states. J Am Chem Soc 2002; 124:5175-82. [PMID: 11982382 DOI: 10.1021/ja0118690] [Citation(s) in RCA: 143] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We have carried out extensive density functional theory (DFT) calculations for possible redox states of the active center in Fe-only hydrogenases. The active center is modeled by [(H(CH(3))S)(CO)(CN(-))Fe(p)(mu-DTN)(mu-CO)Fe(d)(CO)(CN(-))(L)](z)() (z is the net charge in the complex; Fe(p)= the proximal Fe, Fe(d) = the distal Fe, DTN = (-SCH(2)NHCH(2)S-), L is the ligand that bonds with the Fe(d) at the trans position to the bridging CO). Structures of possible redox states are optimized, and CO stretching frequencies are calculated. By a detailed comparison of all the calculated structures and the vibrational frequencies with the available experimental data, we find that (i) the fully oxidized, inactive state is an Fe(II)-Fe(II) state with a hydroxyl (OH(-)) group bonded at the Fe(d), (ii) the oxidized, active state is an Fe(II)-Fe(I) complex which is consistent with the assignment of Cao and Hall (J. Am. Chem. Soc. 2001, 123, 3734), and (iii) the fully reduced state is a mixture with the major component being a protonated Fe(I)-Fe(I) complex and the other component being its self-arranged form, Fe(II)-Fe(II) hydride. Our calculations also show that the exogenous CO can strongly bond with the Fe(II)-Fe(I) species, but cannot bond with the Fe(I)-Fe(I) complex. This result is consistent with experiments that CO tends to inhibit the oxidized, active state, but not the fully reduced state. The electronic structures of all the redox states have been analyzed. It is found that a frontier orbital which is a mixing state between the e(g) of Fe and the 2 pi of the bridging CO plays a key role concerning the reactivity of Fe-only hydrogenases: (i) it is unoccupied in the fully oxidized, inactive state, half-occupied in the oxidized, active state, and fully occupied in the fully reduced state; (ii) the e(g)-2 pi orbital is a bonding state, and this is the key reason for stability of the low oxidation states, such as Fe(I)-Fe(I) complexes; and (iii) in the e(g)-2 pi orbital more charge accumulates between the bridging CO and the Fe(d) than between the bridging CO and the Fe(p), and the occupation increase in this orbital will enhance the bonding between the bridging CO and the Fe(d), leading to the bridging-CO shift toward the Fe(d).
Collapse
Affiliation(s)
- Zhi-Pan Liu
- School of Chemistry, The Queen's University of Belfast, Belfast, BT9 5AG, UK
| | | |
Collapse
|
19
|
Chen Z, Lemon BJ, Huang S, Swartz DJ, Peters JW, Bagley KA. Infrared studies of the CO-inhibited form of the Fe-only hydrogenase from Clostridium pasteurianum I: examination of its light sensitivity at cryogenic temperatures. Biochemistry 2002; 41:2036-43. [PMID: 11827551 DOI: 10.1021/bi011510o] [Citation(s) in RCA: 170] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Infrared spectroscopy has been used to examine the oxidized and CO-inhibited forms of Fe-only hydrogenase I from Clostridium pasteurianum. For the oxidized enzyme, five bands are detected in the infrared spectral region between 2100 and 1800 cm(-1). The pattern of infrared bands is consistent with the presence of two terminally coordinated carbon monoxide molecules, two terminally coordinated cyanide molecules, and one bridging carbon monoxide molecule, ligated to the Fe atoms of the active site [2Fe] subcluster. Infrared spectra of the carbon monoxide-inhibited state, prepared using both natural abundance CO and 13CO, indicate that the two terminally coordinated CO ligands that are intrinsic to the enzyme are coordinated to different Fe atoms of the active site [2Fe] subcluster. Irradiation of the CO-inhibited state at cryogenic temperatures gives rise to two species with dramatically different infrared spectra. The first species has an infrared spectrum identical to the spectrum of the oxidized enzyme, and can be assigned as arising from the photolysis of the exogenous CO from the active site. This species, which has been observed in X-ray crystallographic measurements [Lemon, B. J., and Peters, J. W. (2000) J. Am. Chem. Soc. 122, 3793], decays above 150 K. The second light-induced species decays above 80 K and is characterized by loss of the infrared band associated with the Fe bridging CO at 1809 cm(-1). Potential models for the second photolysis event are discussed.
Collapse
Affiliation(s)
- Zhujun Chen
- Department of Chemistry, Buffalo State, State University of New York, Buffalo, New York 14222, USA
| | | | | | | | | | | |
Collapse
|
20
|
Pereira AS, Tavares P, Moura I, Moura JJ, Huynh BH. Mössbauer characterization of the iron-sulfur clusters in Desulfovibrio vulgaris hydrogenase. J Am Chem Soc 2001; 123:2771-82. [PMID: 11456963 DOI: 10.1021/ja003176+] [Citation(s) in RCA: 120] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The periplasmic hydrogenase of Desulfovibrio vulgaris (Hildenbourough) is an all Fe-containing hydrogenase. It contains two ferredoxin type [4Fe-4S] clusters, termed the F clusters, and a catalytic H cluster. Recent X-ray crystallographic studies on two Fe hydrogenases revealed that the H cluster is composed of two sub-clusters, a [4Fe-4S] cluster ([4Fe-4S](H)) and a binuclear Fe cluster ([2Fe](H)), bridged by a cysteine sulfur. The aerobically purified D. vulgaris hydrogenase is stable in air. It is inactive and requires reductive activation. Upon reduction, the enzyme becomes sensitive to O(2), indicating that the reductive activation process is irreversible. Previous EPR investigations showed that upon reoxidation (under argon) the H cluster exhibits a rhombic EPR signal that is not seen in the as-purified enzyme, suggesting a conformational change in association with the reductive activation. For the purpose of gaining more information on the electronic properties of this unique H cluster and to understand further the reductive activation process, variable-temperature and variable-field Mössbauer spectroscopy has been used to characterize the Fe-S clusters in D. vulgaris hydrogenase poised at different redox states generated during a reductive titration, and in the CO-reacted enzyme. The data were successfully decomposed into spectral components corresponding to the F and H clusters, and characteristic parameters describing the electronic and magnetic properties of the F and H clusters were obtained. Consistent with the X-ray crystallographic results, the spectra of the H cluster can be understood as originating from an exchange coupled [4Fe-4S]-[2Fe] system. In particular, detailed analysis of the data reveals that the reductive activation begins with reduction of the [4Fe-4S](H) cluster from the 2+ to the 1+ state, followed by transfer of the reducing equivalent from the [4Fe-4S](H) subcluster to the binuclear [2Fe](H) subcluster. The results also reveal that binding of exogenous CO to the H cluster affects significantly the exchange coupling between the [4Fe-4S](H) and the [2Fe](H) subclusters. Implication of such a CO binding effect is discussed.
Collapse
Affiliation(s)
- A S Pereira
- Department of Physics, 1021 Rollins Research Building, Emory University, Atlanta, Georgia 30322, USA
| | | | | | | | | |
Collapse
|
21
|
Bennett B, Lemon BJ, Peters JW. Reversible carbon monoxide binding and inhibition at the active site of the Fe-only hydrogenase. Biochemistry 2000; 39:7455-60. [PMID: 10858294 DOI: 10.1021/bi992583z] [Citation(s) in RCA: 118] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Carbon monoxide binding and inhibition have been investigated by electron paramagnetic resonance (EPR) spectroscopy in solution and in crystals of structurally described states of the Fe-only hydrogenase (CpI) from Clostridium pasteurianum. Simulation of the EPR spectrum of the as-isolated state indicates that the main component of the EPR spectrum consists of the oxidized state of the "H cluster" and components due to reduced accessory FeS clusters. Addition of carbon monoxide to CpI in the presence of dithionite results in the inhibition of hydrogen evolution activity, and a characteristic axial EPR signal [g(eff(1)), g(eff(2)), and g(eff(3)) = 2.0725, 2.0061, and 2.0061, respectively] was observed. Hydrogen evolution activity was restored by successive sparging with hydrogen and argon and resulted in samples that exhibited the native oxidized EPR signature that could be converted to the reduced form upon addition of sodium dithionite and hydrogen. To examine the relationship between the spectroscopically defined states of CpI and those observed structurally by X-ray crystallography, we have examined the CpI crystals using EPR spectroscopy. EPR spectra of the crystals in the CO-bound state exhibit the previously described axial signal associated with CO binding. The results indicate that the addition of carbon monoxide to CpI results in a single reversible carbon monoxide-bound species characterized by loss of enzyme activity and the distinctive axial EPR signal.
Collapse
Affiliation(s)
- B Bennett
- Department of Chemistry and Biochemistry, Utah State University, Logan 84322, USA
| | | | | |
Collapse
|
22
|
Lemon BJ, Peters JW. Photochemistry at the Active Site of the Carbon Monoxide Inhibited Form of the Iron-Only Hydrogenase (CpI). J Am Chem Soc 2000. [DOI: 10.1021/ja9943703] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Brian J. Lemon
- Department of Chemistry and Biochemistry Utah State University, Logan, Utah 84322-0300
| | - John W. Peters
- Department of Chemistry and Biochemistry Utah State University, Logan, Utah 84322-0300
| |
Collapse
|
23
|
Abstract
The recent elucidation of the structures of iron-only hydrogenases from the microorganisms Clostridium pasteurianum and Desulfovibrio desulfuricans has revealed that the presumed site of reversible hydrogen oxidation exists as a unique, protein-associated organometallic prosthetic group. Details of the hydrogenase structures provide insight into the chemical mechanism of this highly evolved catalyst.
Collapse
Affiliation(s)
- J W Peters
- Department of Chemistry and Biochemistry, Utah State University, Logan, UT 84322-0300, USA.
| |
Collapse
|
24
|
Lemon BJ, Peters JW. Binding of exogenously added carbon monoxide at the active site of the iron-only hydrogenase (CpI) from Clostridium pasteurianum. Biochemistry 1999; 38:12969-73. [PMID: 10529166 DOI: 10.1021/bi9913193] [Citation(s) in RCA: 263] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A site for the binding of exogenously added carbon monoxide has been identified at the active site of the Fe-only hydrogenase (CpI) from Clostridium pasteurianum. The binding and inhibition of carbon monoxide have been exploited in biochemical and spectroscopic studies to gain mechanistic insights. In the present study, we have taken advantage of the ability to generate an irreversibly carbon monoxide bound state of CpI. The crystallization and structural characterization of CpI inhibited in the presence of carbon monoxide indicates the addition of a single molecule of carbon monoxide. The ability to generate crystals of the carbon monoxide bound state of the hydrogenase that are isomorphous to those of the native enzyme has allowed for a direct comparison of the crystallographic data and an unambiguous identification of the site of carbon monoxide binding at the active site of CpI. Carbon monoxide binds to an Fe atom of the 2Fe subcluster at the site of a terminally bound water molecule in the as crystallized native state of CpI that has been previously suggested to be a potential site of reversible hydrogen oxidation. Binding of carbon monoxide at this site results in an active site that is coordinately saturated with strong ligands (S, CO, and CN), providing a rational potential mechanism for inhibition of reversible hydrogen oxidation at the active site of CpI.
Collapse
Affiliation(s)
- B J Lemon
- Department of Chemistry and Biochemistry, Utah State University, Logan 84322, USA
| | | |
Collapse
|
25
|
Affiliation(s)
- Codrina V. Popescu
- Contribution from the Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213
| | - Eckard Münck
- Contribution from the Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213
| |
Collapse
|
26
|
Staples CR, Ameyibor E, Fu W, Gardet-Salvi L, Stritt-Etter AL, Schürmann P, Knaff DB, Johnson MK. The function and properties of the iron-sulfur center in spinach ferredoxin: thioredoxin reductase: a new biological role for iron-sulfur clusters. Biochemistry 1996; 35:11425-34. [PMID: 8784198 DOI: 10.1021/bi961007p] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Thioredoxin reduction in chloroplasts is catalyzed by a unique class of disulfide reductases which use a [2Fe-2S]2+/+ ferredoxin as the electron donor and contain an Fe-S cluster as the sole prosthetic group in addition to the active-site disulfide. The nature, properties, and function of the Fe-S cluster in spinach ferredoxin:thioredoxin reductase (FTR) have been investigated by the combination of UV/visible absorption, variable-temperature magnetic circular dichroism (MCD), EPR, and resonance Raman (RR) spectroscopies. The results indicate the presence of an S = 0 [4Fe-4S]2+ cluster with complete cysteinyl-S coordination that cannot be reduced at potentials down to -650 mV, but can be oxidized by ferricyanide to an S = 1/2 [4Fe-4S]3+ state (g = 2.09, 2.04, 2.02). The midpoint potential for the [4Fe-4S]3+/2+ couple is estimated to be +420 mV (versus NHE). These results argue against a role for the cluster in mediating electron transport from ferredoxin (Em = -420 mV) to the active-site disulfide (Em = -230 mV, n = 2). An alternative role for the cluster in stabilizing the one-electron-reduced intermediate is suggested by parallel spectroscopic studies of a modified form of the enzyme in which one of the cysteines of the active-site dithiol has been alkylated with N-ethylmaleimide (NEM). NEM-modified FTR is paramagnetic as prepared and exhibits a slow relaxing, S = 1/2 EPR signal, g = 2.11, 2.00, 1.98, that is observable without significant broadening up to 150 K. While the relaxation properties are characteristic of a radical species, MCD, RR, and absorption studies indicate at least partial cluster oxidation to the [4Fe-4S]3+ state. Dye-mediated EPR redox titrations indicate a midpoint potential of -210 mV for the one-electron reduction to a diamagnetic state. By analogy with the properties of the ferricyanide-oxidized [4Fe-4S] cluster in Azotobacter vinelandii 7Fe ferredoxin [Hu, Z., Jollie, D., Burgess, B. K., Stephens, P. J., & Münck, E. (1994) Biochemistry 33, 14475-14485], the spectroscopic and redox properties of NEM-modified FTR are interpreted in terms of a [4Fe-4S]2+ cluster covalently attached through a cluster sulfide to a cysteine-based thiyl radical formed on one of the active-site thiols. A mechanistic scheme for FTR is proposed with similarities to that established for the well-characterized NAD(P)H-dependent flavin-containing disulfide oxidoreductases, but involving sequential one-electron redox processes with the role of the [4Fe-4S]2+ cluster being to stabilize the thiyl radical formed by the initial one-electron reduction of the active-site disulfide. The results indicate a new biological role for Fe-S clusters involving both the stabilization of a thiyl radical intermediate and cluster site-specific chemistry involving a bridging sulfide.
Collapse
Affiliation(s)
- C R Staples
- Department of Chemistry, University of Georgia, Athens 30602, USA
| | | | | | | | | | | | | | | |
Collapse
|
27
|
[38] Mössbauer spectroscopy in study of cytochrome cd1 from Thiobacillus denitrificans, desulfoviridin, and iron hydrogenase. Methods Enzymol 1994. [DOI: 10.1016/0076-6879(94)43040-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
|
28
|
Abstract
Hydrogenases devoid of nickel and containing only Fe-S clusters have been found so far only in some strictly anaerobic bacteria. Four Fe-hydrogenases have been characterized: from Megasphaera elsdenii, Desulfovibrio vulgaris (strain Hildenborough), and two from Clostridium pasteurianum. All contain two or more [4Fe-4S]1+,2+ or F clusters and a unique type of Fe-S center termed the H cluster. The H cluster appears to be remarkably similar in all the hydrogenases, and is proposed as the site of H2 oxidation and H2 production. The F clusters serve to transfer electrons between the H cluster and the external electron carrier. In all of the hydrogenases the H cluster is comprised of at least three Fe atoms, and possibly six. In the oxidized state it contains two types of magnetically distinct Fe atoms, has an S = 1/2 spin state, and exhibits a novel rhombic EPR signal. The reduced cluster is diamagnetic (S = 0). The oxidized H cluster appears to undergo a conformation change upon reduction with H2 with an increase in Fe-Fe distances of about 0.5 A. Studies using resonance Raman, magnetic circular dichroism and electron spin echo spectroscopies suggest that the H cluster has significant non-sulfur coordination. The H cluster has two binding sites for CO, at least one of which can also bind O2. Binding to one site changes the EPR properties of the cluster and gives a photosensitive adduct, but does not affect catalytic activity. Binding to the other site, which only becomes exposed during the catalytic cycle, leads to loss of catalytic activity. Mechanisms of H2 activation and electron transfer are proposed to explain the effects of CO binding and the ability of one of the hydrogenases to preferentially catalyze H2 oxidation.
Collapse
Affiliation(s)
- M W Adams
- Department of Biochemistry, University of Georgia, Athens 30602
| |
Collapse
|
29
|
Adams MW. The metabolism of hydrogen by extremely thermophilic, sulfur-dependent bacteria. FEMS Microbiol Lett 1990. [DOI: 10.1111/j.1574-6968.1990.tb04096.x] [Citation(s) in RCA: 87] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
|
30
|
Conover RC, Kowal AT, Fu WG, Park JB, Aono S, Adams MW, Johnson MK. Spectroscopic characterization of the novel iron-sulfur cluster in Pyrococcus furiosus ferredoxin. J Biol Chem 1990. [DOI: 10.1016/s0021-9258(19)38921-5] [Citation(s) in RCA: 110] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
|
31
|
Zambrano IC, Kowal AT, Mortenson LE, Adams MW, Johnson MK. Magnetic Circular Dichroism and Electron Paramagnetic Resonance Studies of Hydrogenases I and II from Clostridium pasteurianum. J Biol Chem 1989. [DOI: 10.1016/s0021-9258(19)30032-8] [Citation(s) in RCA: 54] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
|