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Curtolo F, Arantes GM. Dissecting Reaction Mechanisms and Catalytic Contributions in Flavoprotein Fumarate Reductases. J Chem Inf Model 2023. [PMID: 37196341 DOI: 10.1021/acs.jcim.3c00292] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
The interconversion between fumarate and succinate is fundamental to the energy metabolism of nearly all organisms. This redox reaction is catalyzed by a large family of enzymes, fumarate reductases and succinate dehydrogenases, using hydride and proton transfers from a flavin cofactor and a conserved Arg side-chain. These flavoenzymes also have substantial biomedical and biotechnological importance. Therefore, a detailed understanding of their catalytic mechanisms is valuable. Here, calibrated electronic structure calculations in a cluster model of the active site of the Fcc3 fumarate reductase were employed to investigate various reaction pathways and possible intermediates in the enzymatic environment and to dissect interactions that contribute to catalysis of fumarate reduction. Carbanion, covalent adduct, carbocation, and radical intermediates were examined. Significantly lower barriers were obtained for mechanisms via carbanion intermediates, with similar activation energies for hydride and proton transfers. Interestingly, the carbanion bound to the active site is best described as an enolate. Hydride transfer is stabilized by a preorganized charge dipole in the active site and by the restriction of the C1-C2 bond in a twisted conformation of the otherwise planar fumarate dianion. But, protonation of a fumarate carboxylate and quantum tunneling effects are not critical for catalysis of the hydride transfer. Calculations also suggest that the driving force for enzyme turnover is provided by regeneration of the catalytic Arg, either coupled with flavin reduction and decomposition of a proposed transient state or directly from the solvent. The detailed mechanistic description of enzymatic reduction of fumarate provided here clarifies previous contradictory views and provides new insights into catalysis by essential flavoenzyme reductases and dehydrogenases.
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Affiliation(s)
- Felipe Curtolo
- Department of Biochemistry, Instituto de Química, Universidade de São Paulo, Av. Prof. Lineu Prestes 748, 05508-900 São Paulo, São Paulo, Brazil
| | - Guilherme M Arantes
- Department of Biochemistry, Instituto de Química, Universidade de São Paulo, Av. Prof. Lineu Prestes 748, 05508-900 São Paulo, São Paulo, Brazil
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2
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Yuan Y, Zhao Y, Yang S, Han S, Lu C, Ji H, Wang T, Ke C, Xu Q, Zhu J, Zhuang X. Modulating intramolecular electron and proton transfer kinetics for promoting carbon dioxide conversion. Chem Commun (Camb) 2022; 58:1966-1969. [PMID: 35044389 DOI: 10.1039/d1cc06731a] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A novel pentagon-heptagon paired azulene group that possesses a large dipole moment is immobilized onto a porphyrin. The as-prepared azulene iron porphyrin exhibits a narrower bandgap and higher electrocatalytic CO2 reduction activity than the pristine iron porphyrin. The maximum CO faradaic efficiency reaches 99.9%, which is the state-of-the-art value among molecular catalysts.
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Affiliation(s)
- Yajie Yuan
- School of Chemical and Environmental Engineering, Shanghai Institute of Technology, Shanghai 201418, China.,The Meso-Entropy Matter Lab, State Key Laboratory of Metal Matrix Composites, School of Chemistry and Chemical Engineering, Frontiers Science Center for Transformative Molecules, Shanghai Jiao Tong University, Shanghai, 200240, China.
| | - Yazhen Zhao
- The Meso-Entropy Matter Lab, State Key Laboratory of Metal Matrix Composites, School of Chemistry and Chemical Engineering, Frontiers Science Center for Transformative Molecules, Shanghai Jiao Tong University, Shanghai, 200240, China.
| | - Shuai Yang
- Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201210, P. R. China
| | - Sheng Han
- School of Chemical and Environmental Engineering, Shanghai Institute of Technology, Shanghai 201418, China
| | - Chenbao Lu
- The Meso-Entropy Matter Lab, State Key Laboratory of Metal Matrix Composites, School of Chemistry and Chemical Engineering, Frontiers Science Center for Transformative Molecules, Shanghai Jiao Tong University, Shanghai, 200240, China.
| | - Huiping Ji
- The Meso-Entropy Matter Lab, State Key Laboratory of Metal Matrix Composites, School of Chemistry and Chemical Engineering, Frontiers Science Center for Transformative Molecules, Shanghai Jiao Tong University, Shanghai, 200240, China.
| | - Tianfu Wang
- The Meso-Entropy Matter Lab, State Key Laboratory of Metal Matrix Composites, School of Chemistry and Chemical Engineering, Frontiers Science Center for Transformative Molecules, Shanghai Jiao Tong University, Shanghai, 200240, China.
| | - Changchun Ke
- Institute of Fuel Cells, School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Qing Xu
- CAS Key Laboratory of Low-Carbon Conversion Science and Engineering, Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai 201210, P. R. China
| | - Jinhui Zhu
- The Meso-Entropy Matter Lab, State Key Laboratory of Metal Matrix Composites, School of Chemistry and Chemical Engineering, Frontiers Science Center for Transformative Molecules, Shanghai Jiao Tong University, Shanghai, 200240, China. .,College of Chemistry, Zhengzhou University, Zhengzhou, Henan 450001, China
| | - Xiaodong Zhuang
- The Meso-Entropy Matter Lab, State Key Laboratory of Metal Matrix Composites, School of Chemistry and Chemical Engineering, Frontiers Science Center for Transformative Molecules, Shanghai Jiao Tong University, Shanghai, 200240, China.
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3
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Chinopoulos C. Succinate in ischemia: Where does it come from? Int J Biochem Cell Biol 2019; 115:105580. [PMID: 31394174 DOI: 10.1016/j.biocel.2019.105580] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2019] [Revised: 07/30/2019] [Accepted: 08/02/2019] [Indexed: 12/20/2022]
Abstract
During tissue ischemia succinate accumulates. Herein, literature spanning the past nine decades is reviewed leaning towards the far greater role of Krebs cycle's canonical activity yielding succinate through α-ketoglutarate -> succinyl-CoA -> succinate even in hypoxia, as opposed to reversal of succinate dehydrogenase. Furthermore, the concepts of i) a diode-like property of succinate dehydrogenase rendering it difficult to reverse, and ii) the absence of mammalian mitochondrial quinones exhibiting redox potentials in the [-60, -80] mV range needed for fumarate reduction, are discussed. Finally, it is emphasized that a "fumarate reductase" enzyme entity reducing fumarate to succinate found in some bacteria and lower eukaryotes remains to be discovered in mammalian mitochondria.
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Affiliation(s)
- Christos Chinopoulos
- Department of Medical Biochemistry, Semmelweis University, Tuzolto st. 37-47, Budapest, 1094, Hungary.
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4
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Modulating the mechanism of electrocatalytic CO 2 reduction by cobalt phthalocyanine through polymer coordination and encapsulation. Nat Commun 2019; 10:1683. [PMID: 30976003 PMCID: PMC6459859 DOI: 10.1038/s41467-019-09626-8] [Citation(s) in RCA: 108] [Impact Index Per Article: 21.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2018] [Accepted: 03/19/2019] [Indexed: 11/24/2022] Open
Abstract
The selective and efficient electrochemical reduction of CO2 to single products is crucial for solar fuels development. Encapsulating molecular catalysts such as cobalt phthalocyanine within coordination polymers such as poly-4-vinylpyridine leads to dramatically increased activity and selectivity for CO2 reduction. In this study, we use a combination of kinetic isotope effect and proton inventory studies to explain the observed increase in activity and selectivity upon polymer encapsulation. We provide evidence that axial-coordination from the pyridyl moieties in poly-4-vinylpyridine to the cobalt phthalocyanine complex changes the rate-determining step in the CO2 reduction mechanism accounting for the increased activity in the catalyst-polymer composite. Moreover, we show that proton delivery to cobalt centers within the polymer is controlled by a proton relay mechanism that inhibits competitive hydrogen evolution. These mechanistic findings provide design strategies for selective CO2 reduction electrocatalysts and serve as a model for understanding the catalytic mechanism of related heterogeneous systems. Understanding the mechanism behind CO2 reduction catalysis is crucial in the development of high efficiency and activity catalysts. Here, authors employ kinetic isotope effects and proton inventory studies to assess catalyst mechanism and proton delivery in molecular CO2 electroreduction materials.
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5
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Maklashina E, Rajagukguk S, Iverson TM, Cecchini G. The unassembled flavoprotein subunits of human and bacterial complex II have impaired catalytic activity and generate only minor amounts of ROS. J Biol Chem 2018; 293:7754-7765. [PMID: 29610278 PMCID: PMC5961047 DOI: 10.1074/jbc.ra118.001977] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2018] [Revised: 03/28/2018] [Indexed: 01/28/2023] Open
Abstract
Complex II (SdhABCD) is a membrane-bound component of mitochondrial and bacterial electron transport chains, as well as of the TCA cycle. In this capacity, it catalyzes the reversible oxidation of succinate. SdhABCD contains the SDHA protein harboring a covalently bound FAD redox center and the iron-sulfur protein SDHB, containing three distinct iron-sulfur centers. When assembly of this complex is compromised, the flavoprotein SDHA may accumulate in the mitochondrial matrix or bacterial cytoplasm. Whether the unassembled SDHA has any catalytic activity, for example in succinate oxidation, fumarate reduction, reactive oxygen species (ROS) generation, or other off-pathway reactions, is not known. Therefore, here we investigated whether unassembled Escherichia coli SdhA flavoprotein, its homolog fumarate reductase (FrdA), and the human SDHA protein have succinate oxidase or fumarate reductase activity and can produce ROS. Using recombinant expression in E. coli, we found that the free flavoproteins from these divergent biological sources have inherently low catalytic activity and generate little ROS. These results suggest that the iron-sulfur protein SDHB in complex II is necessary for robust catalytic activity. Our findings are consistent with those reported for single-subunit flavoprotein homologs that are not associated with iron-sulfur or heme partner proteins.
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Affiliation(s)
- Elena Maklashina
- From the Molecular Biology Division, San Francisco Veterans Affairs Health Care System, San Francisco, California 94121, ,the Department of Biochemistry & Biophysics, University of California, San Francisco, California 94158, and
| | - Sany Rajagukguk
- From the Molecular Biology Division, San Francisco Veterans Affairs Health Care System, San Francisco, California 94121
| | - T. M. Iverson
- the Departments of Pharmacology and ,Biochemistry, ,the Center for Structural Biology, and ,the Vanderbilt Institute of Chemical Biology, Vanderbilt University, Nashville, Tennessee 37232
| | - Gary Cecchini
- From the Molecular Biology Division, San Francisco Veterans Affairs Health Care System, San Francisco, California 94121, ,the Department of Biochemistry & Biophysics, University of California, San Francisco, California 94158, and , Recipient of Senior Research Career Scientist Award IK6BX004215 from the Department of Veterans Affairs. To whom correspondence should be addressed:
Molecular Biology Division (151-S), San Francisco Veterans Affairs Healthcare System, 4150 Clement St., San Francisco, CA 94121. Tel.:
415-221-4810, Ext. 24416; E-mail:
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6
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Marked changes in electron transport through the blue copper protein azurin in the solid state upon deuteration. Proc Natl Acad Sci U S A 2012; 110:507-12. [PMID: 23267087 DOI: 10.1073/pnas.1210457110] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Measuring solid-state electron transport (ETp) across proteins allows studying electron transfer (ET) mechanism(s), while minimizing solvation effects on the process. ETp is, however, sensitive to any static (conformational) or dynamic (vibrational) changes in the protein. Our macroscopic measurements allow extending ETp studies to low temperatures, with the concomitant resolution of lower current densities, because of the larger electrode contact areas. Thus, earlier we reported temperature-independent ETp via the copper protein azurin (Az), from 80 K until denaturation, whereas for apo-Az ETp was temperature dependent above 180 K. Deuteration (H/D substitution) may provide mechanistic information on the question of whether the ETp involves H-bonds in the solid state. Here we report results of kinetic deuterium isotope effect (KIE) measurements on ETp through holo-Az as a function of temperature (30-340 K). Strikingly, deuteration changed ETp from temperature independent to temperature dependent above 180 K. This H/D effect is expressed in KIE values between 1.8 (340 K) and 9.1 (≤ 180 K). These values are remarkable in light of the previously reported inverse KIE on ET in Az in solution. We ascribe the difference between our KIE results and those observed in solution to the dominance of solvent effects in the latter (larger thermal expansion in H(2)O than in D(2)O), whereas in our case the KIE is primarily due to intramolecular changes, mainly in the low-frequency structural modes of the protein caused by H/D exchange. The observed high KIE values are consistent with a transport mechanism that involves through-H-bonds of the β-sheet structure of Az, likely also those in the Cu coordination sphere.
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7
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Zieba AA, Richardson C, Lucero C, Dieng SD, Gindt YM, Schelvis JPM. Evidence for concerted electron proton transfer in charge recombination between FADH- and 306Trp• in Escherichia coli photolyase. J Am Chem Soc 2011; 133:7824-36. [PMID: 21534528 DOI: 10.1021/ja2001488] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Proton-coupled electron-transfer (PCET) is a mechanism of great importance in protein electron transfer and enzyme catalysis, and the involvement of aromatic amino acids in this process is of much interest. The DNA repair enzyme photolyase provides a natural system that allows for the study of PCET using a neutral radical tryptophan (Trp(•)). In Escherichia coli photolyase, photoreduction of the flavin adenine dinucleotide (FAD) cofactor in its neutral radical semiquinone form (FADH(•)) results in the formation of FADH(-) and (306)Trp(•). Charge recombination between these two intermediates requires the uptake of a proton by (306)Trp(•). The rate constant of charge recombination has been measured as a function of temperature in the pH range from 5.5 to 10.0, and the data are analyzed with both classical Marcus and semi-classical Hopfield electron transfer theory. The reorganization energy associated with the charge recombination process shows a pH dependence ranging from 2.3 eV at pH ≤ 7 and 1.2 eV at pH(D) 10.0. These findings indicate that at least two mechanisms are involved in the charge recombination reaction. Global analysis of the data supports the hypothesis that PCET during charge recombination can follow two different mechanisms with an apparent switch around pH 6.5. At lower pH, concerted electron proton transfer (CEPT) is the favorable mechanism with a reorganization energy of 2.1-2.3 eV. At higher pH, a sequential mechanism becomes dominant with rate-limiting electron-transfer followed by proton uptake which has a reorganization energy of 1.0-1.3 eV. The observed 'inverse' deuterium isotope effect at pH < 8 can be explained by a solvent isotope effect that affects the free energy change of the reaction and masks the normal, mass-related kinetic isotope effect that is expected for a CEPT mechanism. To the best of our knowledge, this is the first time that a switch in PCET mechanism has been observed in a protein.
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Affiliation(s)
- Agnieszka A Zieba
- Department of Chemistry and Biochemistry, Montclair State University, 1 Normal Avenue, Montclair, New Jersey 07043, USA
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8
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Fourmond V, Burlat B, Dementin S, Sabaty M, Arnoux P, Étienne É, Guigliarelli B, Bertrand P, Pignol D, Léger C. Dependence of Catalytic Activity on Driving Force in Solution Assays and Protein Film Voltammetry: Insights from the Comparison of Nitrate Reductase Mutants. Biochemistry 2010; 49:2424-32. [DOI: 10.1021/bi902140e] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Vincent Fourmond
- Centre National de la Recherche Scientifique, UPR 9036, Unité de Bioénergétique et Ingénierie des Protéines, Institut de Microbiologie de la Méditerranée, and Aix-Marseille Université, 31 chemin Joseph Aiguier, 13402 Marseille Cedex 20, France
| | - Bénédicte Burlat
- Centre National de la Recherche Scientifique, UPR 9036, Unité de Bioénergétique et Ingénierie des Protéines, Institut de Microbiologie de la Méditerranée, and Aix-Marseille Université, 31 chemin Joseph Aiguier, 13402 Marseille Cedex 20, France
| | - Sébastien Dementin
- Centre National de la Recherche Scientifique, UPR 9036, Unité de Bioénergétique et Ingénierie des Protéines, Institut de Microbiologie de la Méditerranée, and Aix-Marseille Université, 31 chemin Joseph Aiguier, 13402 Marseille Cedex 20, France
| | - Monique Sabaty
- Laboratoire de Bioénergétique Cellulaire, Commissariat à l’Energie Atomique, DSV, IBEB, 13108 Saint-Paul-lez-Durance, France, and Centre National de la Recherche Scientifique, UMR 6191, Biologie Végétale et Microbiologie Environnementale, and Aix-Marseille Université, 13108 Saint-Paul-lez-Durance, France
| | - Pascal Arnoux
- Laboratoire de Bioénergétique Cellulaire, Commissariat à l’Energie Atomique, DSV, IBEB, 13108 Saint-Paul-lez-Durance, France, and Centre National de la Recherche Scientifique, UMR 6191, Biologie Végétale et Microbiologie Environnementale, and Aix-Marseille Université, 13108 Saint-Paul-lez-Durance, France
| | - Émilien Étienne
- Centre National de la Recherche Scientifique, UPR 9036, Unité de Bioénergétique et Ingénierie des Protéines, Institut de Microbiologie de la Méditerranée, and Aix-Marseille Université, 31 chemin Joseph Aiguier, 13402 Marseille Cedex 20, France
| | - Bruno Guigliarelli
- Centre National de la Recherche Scientifique, UPR 9036, Unité de Bioénergétique et Ingénierie des Protéines, Institut de Microbiologie de la Méditerranée, and Aix-Marseille Université, 31 chemin Joseph Aiguier, 13402 Marseille Cedex 20, France
| | - Patrick Bertrand
- Centre National de la Recherche Scientifique, UPR 9036, Unité de Bioénergétique et Ingénierie des Protéines, Institut de Microbiologie de la Méditerranée, and Aix-Marseille Université, 31 chemin Joseph Aiguier, 13402 Marseille Cedex 20, France
| | - David Pignol
- Laboratoire de Bioénergétique Cellulaire, Commissariat à l’Energie Atomique, DSV, IBEB, 13108 Saint-Paul-lez-Durance, France, and Centre National de la Recherche Scientifique, UMR 6191, Biologie Végétale et Microbiologie Environnementale, and Aix-Marseille Université, 13108 Saint-Paul-lez-Durance, France
| | - Christophe Léger
- Centre National de la Recherche Scientifique, UPR 9036, Unité de Bioénergétique et Ingénierie des Protéines, Institut de Microbiologie de la Méditerranée, and Aix-Marseille Université, 31 chemin Joseph Aiguier, 13402 Marseille Cedex 20, France
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9
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ZHANG HN, GUO ZY, GAI PP. Research Progress in Protein Film Voltammetry. CHINESE JOURNAL OF ANALYTICAL CHEMISTRY 2009. [DOI: 10.1016/s1872-2040(08)60093-6] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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10
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Léger C, Bertrand P. Direct Electrochemistry of Redox Enzymes as a Tool for Mechanistic Studies. Chem Rev 2008; 108:2379-438. [DOI: 10.1021/cr0680742] [Citation(s) in RCA: 594] [Impact Index Per Article: 37.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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11
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Bertrand P, Frangioni B, Dementin S, Sabaty M, Arnoux P, Guigliarelli B, Pignol D, Léger C. Effects of Slow Substrate Binding and Release in Redox Enzymes: Theory and Application to Periplasmic Nitrate Reductase. J Phys Chem B 2007; 111:10300-11. [PMID: 17676894 DOI: 10.1021/jp074340j] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
For redox enzymes, the technique called protein film voltammetry makes it possible to determine the entire profile of activity against driving force by having the enzyme exchanging directly electrons with the rotating-disc electrode onto which it is adsorbed. Both the potential location of the catalytic response and its detailed shape report on the sequence of catalytic events, electron transfers and chemical steps, but the models that have been used so far to decipher this signal lack generality. For example, it was often proposed that substrate binding to multiple redox states of the active site may explain that turnover is greater in a certain window of electrode potential, but no fully analytical treatment has been given. Here, we derive (i) the general current equation for the case of reversible substrate binding to any redox states of a two-electron active site (as exemplified by flavins and Mo cofactors), (ii) the quantitative conditions for an extremum in activity to occur, and (iii) the expressions from which the substrate-concentration dependence of the catalytic potential can be interpreted to learn about the kinetics of substrate binding and how this affects the reduction potential of the active site. Not only does slow substrate binding and release make the catalytic wave shape highly complex, but we also show that it can have important consequences which will escape detection in traditional experiments: the position of the wave (this is the driving force that is required to elicit catalysis) departs from the reduction potential of the active site even at the lowest substrate concentration, and this deviation may be large if substrate binding is irreversible. This occurs in the reductive half-cycle of periplasmic nitrate reductase where irreversibility lowers the driving force required to reduce the active site under turnover conditions and favors intramolecular electron transfer from the proximal [4Fe4S]+ cluster to the active site Mo(V).
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Affiliation(s)
- Patrick Bertrand
- Laboratoire de Bioénergétique et Ingénierie des Protéines, CNRS UPR 9036, IBSM, France
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12
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Gwyer JD, Zhang J, Butt JN, Ulstrup J. Voltammetry and in situ scanning tunneling microscopy of cytochrome C nitrite reductase on Au(111) electrodes. Biophys J 2006; 91:3897-906. [PMID: 16935959 PMCID: PMC1630480 DOI: 10.1529/biophysj.106.089755] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2006] [Accepted: 08/15/2006] [Indexed: 11/18/2022] Open
Abstract
Escherichia coli cytochrome c nitrite reductase (NrfA) catalyzes the six-electron reduction of nitrite to perform an important role in the biogeochemical cycling of nitrogen. Here we describe NrfA adsorption on single-crystal Au(111) electrodes as an electrocatalytically active film in which the enzyme undergoes direct electron exchange with the electrode. The adsorbed NrfA has been imaged to molecular resolution by in situ scanning tunneling microscopy (in situ STM) under full electrochemical potential control and under conditions where the enzyme is electrocatalytically active. Details of the density and orientational distribution of NrfA molecules are disclosed. The submonolayer coverage resolved by in situ STM is readily reconciled with the failure to detect nonturnover signals in cyclic voltammetry of the NrfA films. The molecular structures show a range of lateral dimensions. These are suggestive of a distribution of orientations that could account for the otherwise anomalously low turnover number calculated for the total population of adsorbed NrfA molecules when compared with that determined for solutions of NrfA. Thus, comparison of the voltammetric signals and in situ STM images offers a direct approach to correlate electrocatalytic and molecular properties of the protein layer, a long-standing issue in protein film voltammetry.
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Affiliation(s)
- James D Gwyer
- School of Chemical Sciences and Pharmacy, and School of Biological Sciences, Centre for Metalloprotein Spectroscopy and Biology, University of East Anglia, Norwich NR4 7TJ, United Kingdom
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13
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Hirst J. Elucidating the mechanisms of coupled electron transfer and catalytic reactions by protein film voltammetry. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2006; 1757:225-39. [PMID: 16730325 DOI: 10.1016/j.bbabio.2006.04.002] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/01/2006] [Revised: 03/28/2006] [Accepted: 04/01/2006] [Indexed: 11/30/2022]
Abstract
Protein film voltammetry, the direct electrochemistry of redox enzymes and proteins, provides precise and comprehensive information on complicated reaction mechanisms. By controlling the driving force for a reaction (using the applied potential) and monitoring the reaction in real time (using the current), it allows thermodynamic and kinetic information to be determined simultaneously. Two challenges are inherent to protein film voltammetry: (i) to adsorb the protein or enzyme in a native and active configuration on the electrode surface, and (ii) to understand and interpret voltammetric results on both a qualitative and quantitative level, allowing mechanistic models to be proposed and rigorous experiments to test these models to be devised. This review focuses on the second of these two challenges. It describes how to use protein film voltammetry to derive mechanistic and biochemically relevant information about redox proteins and enzymes, and how to evaluate and interpret voltammetric results. Selected key studies are described in detail, to illustrate their underlying principles, strategies and physical interpretations.
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Affiliation(s)
- Judy Hirst
- Medical Research Council Dunn Human Nutrition Unit, Wellcome Trust/MRC Building, Hills Road, Cambridge, CB2 2XY, UK.
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14
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Vincent KA, Armstrong FA. Investigating metalloenzyme reactions using electrochemical sweeps and steps: fine control and measurements with reactants ranging from ions to gases. Inorg Chem 2005; 44:798-809. [PMID: 15859247 DOI: 10.1021/ic048519+] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Protein film voltammetry is a powerful method for probing the chemistry of redox-active sites in metalloproteins. The technique affords precise potential control over a tiny quantity of material that is manipulated on an electrode surface, providing information on ligand- or metal-exchange reactions coupled to electron transfer. This is illustrated by examples of transformations of the iron-sulfur clusters in ferredoxins. Protein film voltammetry is particularly advantageous in studies of metalloenzymes for which the current response is proportional to catalytic activity: kinetic data of extremely high signal/noise ratio are obtained for highly active enzymes. We present a series of interesting examples in which catalytic activity varies in unusual ways with applied potential, surveying information that can be obtained from cyclic voltammetry and then looking beyond this method to controlled potential-step experiments that yield kinetic and mechanistic details. Recent results on the voltammetry of the highly active [NiFe]-hydrogenase from Allochromatium vinosum illustrate how it is possible to use the precise kinetic information from potential-step experiments to diagnose subtle details of transformations between catalytically active and inactive states of an enzyme. Protein film voltammetry thus complements spectroscopic techniques and other physical methods, revealing the chemistry of systems that might appear intractable or convoluted by other means.
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Affiliation(s)
- Kylie A Vincent
- Department of Chemistry, Inorganic Chemistry Laboratory, University of Oxford, Oxford OX1 3QR, England
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15
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Battistuzzi G, Borsari M, Ranieri A, Sola M. Solvent-based deuterium isotope effects on the redox thermodynamics of cytochrome c. J Biol Inorg Chem 2004; 9:781-7. [PMID: 15278784 DOI: 10.1007/s00775-004-0580-x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2004] [Accepted: 06/29/2004] [Indexed: 10/26/2022]
Abstract
The reduction thermodynamics of cytochrome c (cytc), determined electrochemically, are found to be sensitive to solvent H/D isotope effects. Reduction of cytochrome c is enthalpically more favored in D(2)O with respect to H(2)O, but is disfavored on entropic grounds. This is consistent with a reduction-induced strengthening of the H-bonding network within the hydration sphere of the protein. No significant changes in E degrees ' occur, since the above variations are compensative. As a main result, this work shows that the oxidation-state-dependent differences in protein solvation, including electrostatics and solvent reorganization effects, play an important role in determining the individual enthalpy and entropy changes of the reduction process. It is conceivable that this is a common thermodynamic feature of all electron transport metalloproteins. The isotope effects turn out to be sensitive to buffer anions which specifically bind to cytc. Evidence is gained that the solvation thermodynamics of both redox forms of cytc are sensibly affected by strongly hydrated anions.
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Affiliation(s)
- G Battistuzzi
- Department of Chemistry and Centro SCS, University of Modena and Reggio Emilia, Via Campi 183, 41100 Modena, Italy
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Wijma HJ, Canters GW, de Vries S, Verbeet MP. Bidirectional Catalysis by Copper-Containing Nitrite Reductase. Biochemistry 2004; 43:10467-74. [PMID: 15301545 DOI: 10.1021/bi0496687] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The copper-containing nitrite reductase from Alcaligenes faecalis S-6 was found to catalyze the oxidation of nitric oxide to nitrite, the reverse of its physiological reaction. Thermodynamic and kinetic constants with the physiological electron donor pseudoazurin were determined for both directions of the catalyzed reaction in the pH range of 6-8. For this, nitric oxide was monitored by a Clark-type electrode, and the redox state of pseudoazurin was measured by optical spectroscopy. The equilibrium constant (K(eq)) depends on the reduction potentials of pseudoazurin and nitrite/nitric oxide, both of which vary with pH. Above pH 6.2 the formation of NiR substrates (nitrite and reduced pseudoazurin) is favored over the products (NO and oxidized pseudoazurin). At pH 8 the K(eq) amounts to 10(3). The results show that dissimilatory nitrite reductases catalyze an unfavorable reaction at physiological pH (pH = 7-8). Consequently, nitrous oxide production by copper-containing nitrite reductases is unlikely to occur in vivo with a native electron donor. With increasing pH, the rate and specificity constant of the forward reaction decrease and become lower than the rate of the reverse reaction. The opposite occurs for the rate of the reverse reaction; thus the catalytic bias for nitrite reduction decreases. At pH 6.0 the k(cat) for nitrite reduction was determined to be 1.5 x 10(3) s(-1), and at pH 8 the rate of the reverse reaction is 125 s(-1).
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Affiliation(s)
- Hein J Wijma
- Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands
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17
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Catalysis by immobilized redox enzymes. Diagnosis of inactivation and reactivation effects through odd cyclic voltammetric responses. J Electroanal Chem (Lausanne) 2004. [DOI: 10.1016/j.jelechem.2003.07.035] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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18
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Abstract
Complex II is the only membrane-bound component of the Krebs cycle and in addition functions as a member of the electron transport chain in mitochondria and in many bacteria. A recent X-ray structural solution of members of the complex II family of proteins has provided important insights into their function. One feature of the complex II structures is a linear electron transport chain that extends from the flavin and iron-sulfur redox cofactors in the membrane extrinsic domain to the quinone and b heme cofactors in the membrane domain. Exciting recent developments in relation to disease in humans and the formation of reactive oxygen species by complex II point to its overall importance in cellular physiology.
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Affiliation(s)
- Gary Cecchini
- Molecular Biology Division, Veterans Administration Medical Center, San Francisco, California 94121, USA.
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Léger C, Elliott SJ, Hoke KR, Jeuken LJC, Jones AK, Armstrong FA. Enzyme electrokinetics: using protein film voltammetry to investigate redox enzymes and their mechanisms. Biochemistry 2003; 42:8653-62. [PMID: 12873124 DOI: 10.1021/bi034789c] [Citation(s) in RCA: 204] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Protein film voltammetry is a relatively new approach to studying redox enzymes, the concept being that a sample of a redox protein is configured as a film on an electrode and probed by a variety of electrochemical techniques. The enzyme molecules are bound at the electrode surface in such a way that there is fast electron transfer and complete retention of the chemistry of the active site that is observed in more conventional experiments. Modulations of the electrode potential or catalytic turnover result in the movement of electrons to, from, and within the enzyme; this is detected as a current that varies in characteristic ways with time and potential. Henceforth, the potential dimension is introduced into enzyme kinetics. The presence of additional intrinsic redox centers for providing fast intramolecular electron transfer between a buried active site and the protein surface is an important factor. Centers which carry out cooperative two-electron transfer, most obviously flavins, produce a particularly sharp signal that allows them to be observed, even as transient states, when spectroscopic methods are not useful. High catalytic activity produces a large amplification of the current, and useful information can be obtained even if the coverage on the electrode is low. Certain enzymes display optimum activity at a particular potential, and this can be both mechanistically informative and physiologically relevant. This paper outlines the principles of protein film voltammetry by discussing some recent results from this laboratory.
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Affiliation(s)
- Christophe Léger
- Inorganic Chemistry Laboratory, Oxford University, South Parks Road, Oxford OX1 3QR, UK
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20
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Jeuken LJC. Conformational reorganisation in interfacial protein electron transfer. BIOCHIMICA ET BIOPHYSICA ACTA 2003; 1604:67-76. [PMID: 12765764 DOI: 10.1016/s0005-2728(03)00026-4] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Protein-protein electron transfer (ET) plays an essential role in all redox chains. Earlier studies which used cross-linking and increased solution viscosity indicated that the rate of many ET reactions is limited (i.e., gated) by conformational reorientations at the surface interface. These results are later supported by structural studies using NMR and molecular modelling. New insights into conformational gating have also come from electrochemical experiments in which proteins are noncovalently adsorbed on the electrode surface. These systems have the advantage that it is relatively easy to vary systematically the driving force and electronic coupling. In this review we summarize the current knowledge obtained from these electrochemical experiments and compare it with some of the results obtained for protein-protein ET.
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21
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Léger C, Jones AK, Albracht SPJ, Armstrong FA. Effect of a Dispersion of Interfacial Electron Transfer Rates on Steady State Catalytic Electron Transport in [NiFe]-hydrogenase and Other Enzymes. J Phys Chem B 2002. [DOI: 10.1021/jp0265687] [Citation(s) in RCA: 217] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Christophe Léger
- Inorganic Chemistry Laboratory, South Parks Road, Oxford OX1 3QR, United Kingdom, and Swammerdam Institute for Life Sciences, Biochemistry, University of Amsterdam, Plantage Muidergracht 12, NL-1018 TV Amsterdam, The Netherlands
| | - Anne K. Jones
- Inorganic Chemistry Laboratory, South Parks Road, Oxford OX1 3QR, United Kingdom, and Swammerdam Institute for Life Sciences, Biochemistry, University of Amsterdam, Plantage Muidergracht 12, NL-1018 TV Amsterdam, The Netherlands
| | - Simon P. J. Albracht
- Inorganic Chemistry Laboratory, South Parks Road, Oxford OX1 3QR, United Kingdom, and Swammerdam Institute for Life Sciences, Biochemistry, University of Amsterdam, Plantage Muidergracht 12, NL-1018 TV Amsterdam, The Netherlands
| | - Fraser A. Armstrong
- Inorganic Chemistry Laboratory, South Parks Road, Oxford OX1 3QR, United Kingdom, and Swammerdam Institute for Life Sciences, Biochemistry, University of Amsterdam, Plantage Muidergracht 12, NL-1018 TV Amsterdam, The Netherlands
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22
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Léger C, Heffron K, Pershad HR, Maklashina E, Luna-Chavez C, Cecchini G, Ackrell BA, Armstrong FA. Enzyme electrokinetics: energetics of succinate oxidation by fumarate reductase and succinate dehydrogenase. Biochemistry 2001; 40:11234-45. [PMID: 11551223 DOI: 10.1021/bi010889b] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Protein film voltammetry is used to probe the energetics of electron transfer and substrate binding at the active site of a respiratory flavoenzyme--the membrane-extrinsic catalytic domain of Escherichia coli fumarate reductase (FrdAB). The activity as a function of the electrochemical driving force is revealed in catalytic voltammograms, the shapes of which are interpreted using a Michaelis-Menten model that incorporates the potential dimension. Voltammetric experiments carried out at room temperature under turnover conditions reveal the reduction potentials of the FAD, the stability of the semiquinone, relevant protonation states, and pH-dependent succinate--enzyme binding constants for all three redox states of the FAD. Fast-scan experiments in the presence of substrate confirm the value of the two-electron reduction potential of the FAD and show that product release is not rate limiting. The sequence of binding and protonation events over the whole catalytic cycle is deduced. Importantly, comparisons are made with the electrocatalytic properties of SDH, the membrane-extrinsic catalytic domain of mitochondrial complex II.
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Affiliation(s)
- C Léger
- Inorganic Chemistry Laboratory, Oxford OX1 3QR, U.K
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23
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Heffron K, Léger C, Rothery RA, Weiner JH, Armstrong FA. Determination of an optimal potential window for catalysis by E. coli dimethyl sulfoxide reductase and hypothesis on the role of Mo(V) in the reaction pathway. Biochemistry 2001; 40:3117-26. [PMID: 11258926 DOI: 10.1021/bi002452u] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Protein film voltammetry (PFV) of Escherichia coli dimethyl sulfoxide (DMSO) reductase (DmsABC) adsorbed at a graphite electrode reveals that the catalytic activity of this complex Mo-pterin/Fe-S enzyme is optimized within a narrow window of electrode potential. The upper and lower limits of this window are determined from the potential dependences of catalytic activity in reducing and oxidizing directions; i.e., for reduction of DMSO (or trimethylamine-N-oxide) and oxidation of trimethylphosphine (PMe(3)). At either limit, the catalytic activity drops despite the increase in driving force: as the potential is lowered below -200 mV (pH 7.0-8.9), the rate of reduction of DMSO decreases abruptly, while for PMe(3), an oxidative current is observed that vanishes as the potential is raised above +20 mV (pH 9.0). Analysis of the waveshapes reveals that both activity thresholds result from one-electron redox reactions that arise, most likely, from groups within the enzyme; if so, they represent "switches" that reflect the catalytic mechanism and may be of physiological relevance. The potential window of activity coincides approximately with the appearance of the Mo(V) EPR signal observed in potentiometric titrations, suggesting that crucial stages of catalysis are facilitated while the active site is in the intermediate Mo(V) oxidation state.
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Affiliation(s)
- K Heffron
- Inorganic Chemistry Laboratory, Oxford University, South Parks Road, Oxford, OX1 3QR, United Kingdom
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Furdui C, Ragsdale SW. The role of pyruvate ferredoxin oxidoreductase in pyruvate synthesis during autotrophic growth by the Wood-Ljungdahl pathway. J Biol Chem 2000; 275:28494-9. [PMID: 10878009 DOI: 10.1074/jbc.m003291200] [Citation(s) in RCA: 122] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Pyruvate:ferredoxin oxidoreductase (PFOR) catalyzes the oxidative decarboxylation of pyruvate to acetyl-CoA and CO(2). The catalytic proficiency of this enzyme for the reverse reaction, pyruvate synthase, is poorly understood. Conversion of acetyl-CoA to pyruvate links the Wood-Ljungdahl pathway of autotrophic CO(2) fixation to the reductive tricarboxylic acid cycle, which in these autotrophic anaerobes is the stage for biosynthesis of all cellular macromolecules. The results described here demonstrate that the Clostridium thermoaceticum PFOR is a highly efficient pyruvate synthase. The Michaelis-Menten parameters for pyruvate synthesis by PFOR are: V(max) = 1.6 unit/mg (k(cat) = 3.2 s(-1)), K(m)(Acetyl-CoA) = 9 micrometer, and K(m)(CO(2)) = 2 mm. The intracellular concentrations of acetyl-CoA, CoASH, and pyruvate have been measured. The predicted rate of pyruvate synthesis at physiological concentrations of substrates clearly is sufficient to support the role of PFOR as a pyruvate synthase in vivo. Measurements of its k(cat)/K(m) values demonstrate that ferredoxin is a highly efficient electron carrier in both the oxidative and reductive reactions. On the other hand, rubredoxin is a poor substitute in the oxidative direction and is inept in donating electrons for pyruvate synthesis.
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Affiliation(s)
- C Furdui
- Department of Biochemistry, Beadle Center, University of Nebraska, Lincoln, Nebraska 68588-0664, USA
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26
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Pershad HR, Hirst J, Cochran B, Ackrell BA, Armstrong FA. Voltammetric studies of bidirectional catalytic electron transport in Escherichia coli succinate dehydrogenase: comparison with the enzyme from beef heart mitochondria. BIOCHIMICA ET BIOPHYSICA ACTA 1999; 1412:262-72. [PMID: 10482788 DOI: 10.1016/s0005-2728(99)00066-3] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
The succinate dehydrogenases (SDH: soluble, membrane-extrinsic subunits of succinate:quinone oxidoreductases) from Escherichia coli and beef heart mitochondria each adsorb at a pyrolytic graphite 'edge' electrode and catalyse the interconversion of succinate and fumarate according to the electrochemical potential that is applied. E. coli and beef heart mitochondrial SDH share only ca. 50% homology, yet the steady-state catalytic activities, when measured over a continuous potential range, display very similar catalytic operating potentials and energetic biases (the relative ability to catalyse succinate oxidation vs. fumarate reduction). Importantly, E. coli SDH also exhibits the interesting 'tunnel-diode' behaviour previously reported for the mitochondrial enzyme. Thus as the potential is lowered below ca. -60 mV (pH 7, 38 degrees C) the rate of catalytic fumarate reduction decreases abruptly despite an increase in driving force. Since the homology relates primarily to residues associated with active site regions, the marked similarity in the voltammetry reaffirms our previous conclusions that the tunnel-diode behaviour is a characteristic property of the enzyme active site. Thus, succinate dehydrogenase is an excellent fumarate reductase, but its activity in this direction is limited to a very specific range of potential.
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Affiliation(s)
- H R Pershad
- Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford, UK
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27
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Pershad HR, Duff JL, Heering HA, Duin EC, Albracht SP, Armstrong FA. 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 1999; 38:8992-9. [PMID: 10413472 DOI: 10.1021/bi990108v] [Citation(s) in RCA: 198] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The nickel-iron hydrogenase from Chromatium vinosum adsorbs at a pyrolytic graphite edge-plane (PGE) electrode and catalyzes rapid interconversion of H(+)((aq)) and H(2) at potentials expected for the half-cell reaction 2H(+) right arrow over left arrow H(2), 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 H(2) is extremely rapid; at 10% partial pressure H(2), mass transport control persists even at the highest electrode rotation rates. The turnover number for H(2) oxidation lies in the range of 1500-9000 s(-)(1) at 30 degrees 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 allows improved definition of signals that can be attributed to the reversible (non-turnover) oxidation and reduction of redox centers. One signal, at -30 mV vs SHE (pH 7.0, 30 degrees C), is assigned to the [3Fe-4S](+/0) cluster on the basis of potentiometric measurements. The second, at -301 mV and having a 1. 5-2.5-fold greater amplitude, is tentatively assigned to the two [4Fe-4S](2+/+) clusters with similar reduction potentials. No other redox couples are observed, suggesting that these two sets of centers are the only ones in CO-inhibited hydrogenase capable of undergoing simple rapid cycling of their redox states. With the buried NiFe active site very unlikely to undergo direct electron exchange with the electrode, at least one and more likely each of the three iron-sulfur clusters must serve as relay sites. The fact that H(2) oxidation is rapid even at potentials nearly 300 mV more negative than the reduction potential of the [3Fe-4S](+/0) cluster shows that its singularly high equilibrium reduction potential does not compromise catalytic efficiency.
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Affiliation(s)
- H R Pershad
- Department of Chemistry, Oxford University, U.K
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28
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Turner KL, Doherty MK, Heering HA, Armstrong FA, Reid GA, Chapman SK. Redox properties of flavocytochrome c3 from Shewanella frigidimarina NCIMB400. Biochemistry 1999; 38:3302-9. [PMID: 10079073 DOI: 10.1021/bi9826308] [Citation(s) in RCA: 71] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The thermodynamic and catalytic properties of flavocytochrome c3 from Shewanella frigidimarina have been studied using a combination of protein film voltammetry and solution methods. As measured by solution kinetics, maximum catalytic efficiencies for fumarate reduction (kcat/Km = 2.1 x 10(7) M-1 s-1 at pH 7.2) and succinate oxidation (kcat/Km = 933 M-1 s-1 at pH 8.5) confirm that flavocytochrome c3 is a unidirectional fumarate reductase. Very similar catalytic properties are observed for the enzyme adsorbed to monolayer coverage at a pyrolytic graphite "edge" electrode, thus confirming the validity of the electrochemical method for providing complementary information. In the absence of fumarate, the adsorbed enzyme displays a complex envelope of reversible redox signals which can be deconvoluted to yield the contributions from each active site. Importantly, the envelope is dominated by the two-electron signal due to FAD [E degrees ' = -152 mV vs the standard hydrogen electrode (SHE) at pH 7.0 and 24 degrees C] which enables quantitative examination of this center, the visible spectrum of which is otherwise masked by the intense absorption bands due to the hemes. The FAD behaves as a cooperative two-electron center with a pH-dependent reduction potential that is modulated (pKox at 6.5) by ionization of a nearby residue. In conjunction with the kinetic pKa values determined for the forward and reverse reactions (7.4 and 8.6, respectively), a mechanism for fumarate reduction, incorporating His365 and an anionic form of reduced FAD, is proposed. The reduction potentials of the four heme groups, estimated by analysis of the underlying envelope, are -102, -146, -196, and -238 mV versus the SHE at pH 7.0 and 24 degrees C and are comparable to those determined by redox potentiometry.
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Affiliation(s)
- K L Turner
- Department of Chemistry, University of Edinburgh, Scotland
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29
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Mondal MS, Goodin DB, Armstrong FA. Simultaneous Voltammetric Comparisons of Reduction Potentials, Reactivities, and Stabilities of the High-Potential Catalytic States of Wild-Type and Distal-Pocket Mutant (W51F) Yeast Cytochrome c Peroxidase. J Am Chem Soc 1998. [DOI: 10.1021/ja980197j] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Madhu S. Mondal
- Contribution from the Inorganic Chemistry Laboratory, Oxford University, South Parks Road, Oxford OX1 3QR, England, and The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037
| | - David B. Goodin
- Contribution from the Inorganic Chemistry Laboratory, Oxford University, South Parks Road, Oxford OX1 3QR, England, and The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037
| | - Fraser A. Armstrong
- Contribution from the Inorganic Chemistry Laboratory, Oxford University, South Parks Road, Oxford OX1 3QR, England, and The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037
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30
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Heering HA, Weiner JH, Armstrong FA. Direct Detection and Measurement of Electron Relays in a Multicentered Enzyme: Voltammetry of Electrode-Surface Films of E. coli Fumarate Reductase, an Iron−Sulfur Flavoprotein. J Am Chem Soc 1997. [DOI: 10.1021/ja9723242] [Citation(s) in RCA: 90] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Hendrik A. Heering
- Contribution from the Inorganic Chemistry Laboratory, Oxford University, South Parks Road, Oxford OX1 3QR, England, and Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2H7
| | - Joel H. Weiner
- Contribution from the Inorganic Chemistry Laboratory, Oxford University, South Parks Road, Oxford OX1 3QR, England, and Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2H7
| | - Fraser A. Armstrong
- Contribution from the Inorganic Chemistry Laboratory, Oxford University, South Parks Road, Oxford OX1 3QR, England, and Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2H7
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