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Lindahl PA, Vali SW. Mössbauer-based molecular-level decomposition of the Saccharomyces cerevisiae ironome, and preliminary characterization of isolated nuclei. Metallomics 2022; 14:mfac080. [PMID: 36214417 PMCID: PMC9624242 DOI: 10.1093/mtomcs/mfac080] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2022] [Accepted: 09/23/2022] [Indexed: 11/25/2022]
Abstract
One hundred proteins in Saccharomyces cerevisiae are known to contain iron. These proteins are found mainly in mitochondria, cytosol, nuclei, endoplasmic reticula, and vacuoles. Cells also contain non-proteinaceous low-molecular-mass labile iron pools (LFePs). How each molecular iron species interacts on the cellular or systems' level is underdeveloped as doing so would require considering the entire iron content of the cell-the ironome. In this paper, Mössbauer (MB) spectroscopy was used to probe the ironome of yeast. MB spectra of whole cells and isolated organelles were predicted by summing the spectral contribution of each iron-containing species in the cell. Simulations required input from published proteomics and microscopy data, as well as from previous spectroscopic and redox characterization of individual iron-containing proteins. Composite simulations were compared to experimentally determined spectra. Simulated MB spectra of non-proteinaceous iron pools in the cell were assumed to account for major differences between simulated and experimental spectra of whole cells and isolated mitochondria and vacuoles. Nuclei were predicted to contain ∼30 μM iron, mostly in the form of [Fe4S4] clusters. This was experimentally confirmed by isolating nuclei from 57Fe-enriched cells and obtaining the first MB spectra of the organelle. This study provides the first semi-quantitative estimate of all concentrations of iron-containing proteins and non-proteinaceous species in yeast, as well as a novel approach to spectroscopically characterizing LFePs.
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Affiliation(s)
- Paul A Lindahl
- Department of Chemistry, Texas A&M University, College Station, TX,USA
- Department of Biochemistry and Biophysics, Texas A&M University, College Station TX,USA
| | - Shaik Waseem Vali
- Department of Chemistry, Texas A&M University, College Station, TX,USA
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2
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3
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Carter EL, Proshlyakov DA, Hausinger RP. Apoprotein isolation and activation, and vibrational structure of the Helicobacter mustelae iron urease. J Inorg Biochem 2011; 111:195-202. [PMID: 22196017 DOI: 10.1016/j.jinorgbio.2011.10.016] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2011] [Revised: 10/18/2011] [Accepted: 10/26/2011] [Indexed: 02/08/2023]
Abstract
The micro aerophilic pathogen Helicobacter mustelae synthesizes an oxygen-labile, iron-containing urease (UreA2B2) in addition to its standard nickel-containing enzyme (UreAB). An apoprotein form of the iron urease was prepared from ureA2B2-expressing recombinant Escherichia coli cells that were grown in minimal medium. Temperature-dependent circular dichroism measurements of holoprotein and apoprotein demonstrate an enhancement of thermal stability associated with the UreA2B2 metallocenter. In parallel to the situation reported for nickel activation of the standard urease apoprotein, incubation of UreA2B2 apoprotein with ferrous ions and bicarbonate generated urease activity in a portion of the nascent active sites. In addition, ferrous ions were shown to be capable of reductively activating the oxidized metallocenter. Resonance Raman spectra of the inactive, aerobically-purified UreA2B2 holoprotein exhibit vibrations at 495cm(-1) and 784cm(-1), consistent with ν(s) and ν(as) modes of an Fe(III)OFe(III) center; these modes undergo downshifts upon binding of urea and were unaffected by changes in pH. The low-frequency mode also exhibits an isotopic shift from 497 to 476cm(-1) upon (16)O/(18)O bulk water isotope substitution. Expression of subunits of the conventional nickel-containing Klebsiella aerogenes urease in cells grown in rich medium without nickel resulted in iron incorporation into a portion of the protein. The inactive iron-loaded species exhibited a UV-visible spectrum similar to oxidized UreA2B2 and was capable of being reductively activated under anoxic conditions. Results from these studies more clearly define the formation and unique properties of the iron urease metallocenter.
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Affiliation(s)
- Eric L Carter
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, MI 48824, USA
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4
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Das S, Bhattacharyya J, Mukhopadhyay S. Mechanistic studies on oxidation of hydrogen peroxide by an oxo-bridged diiron complex in aqueous acidic media. Dalton Trans 2008:6634-40. [DOI: 10.1039/b810011j] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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5
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Que L, True AE. Dinuclear Iron- and Manganese-Oxo Sites in Biology. PROGRESS IN INORGANIC CHEMISTRY 2007. [DOI: 10.1002/9780470166390.ch3] [Citation(s) in RCA: 213] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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6
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Diiron(II) complexes showing a reversible oxygenation induced by a proton transfer mediated with a water molecule. Biological implication of a water molecule in hemerythrin function. J Organomet Chem 2007. [DOI: 10.1016/j.jorganchem.2006.04.052] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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7
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Kryatov SV, Rybak-Akimova EV, Schindler S. Kinetics and Mechanisms of Formation and Reactivity of Non-heme Iron Oxygen Intermediates. Chem Rev 2005; 105:2175-226. [PMID: 15941212 DOI: 10.1021/cr030709z] [Citation(s) in RCA: 329] [Impact Index Per Article: 17.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Sergey V Kryatov
- Department of Chemistry, Tufts University, Medford, Massachusetts 02155, USA
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Bhattacharyya J, Dutta K, Mukhopadhyay S. Mechanistic studies on oxidation of hydrazine by a µ-oxo diiron(iii,iii) complex in aqueous acidic media—proton coupled electron transfer. Dalton Trans 2004:2910-7. [PMID: 15349166 DOI: 10.1039/b407980a] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
[Fe2(mu-O)(phen)4(H2O)2]4+ (1), one of the simplest mu-oxo diiron(III) complexes, quantitatively oxidises hydrazine to dinitrogen and itself is reduced to two moles of ferroin, [Fe(phen)3]2+ in presence of excess phenanthroline. The weak dibasic acid, 1 (pKa1= 3.71 +/- 0.05 and pKa2= 5.28 +/- 0.10 at 25.0 degrees C, I= 1.0 mol dm(-3)(NaNO3)) and its conjugate bases, [Fe2(mu-O)(phen)4(H2O)(OH)]3+ (2) and [Fe2(mu-O)(phen)4(OH)2]2+ (3) are involved in the redox process with the reactivity order 1 > 2 > 3 whereas N2H4 and not N2H5+ was found to be reactive in the pH interval studied 3.45-5.60. Cyclic voltammetric studies indicate poor oxidizing capacity of the title substitution-labile diiron complex, yet it oxidizes N2H4 with a moderate rate--a proton coupled electron transfer (1e, 1H+) drags the energetically unfavourable reaction to completion. The rate retardation in D2O media is substantially higher at higher pH due to the increasing basicity of the oxo-ligand in the order 3 > 2 > 1. Marcus calculations result an unacceptably high one-electron self-exchange rate for the iron center indicating an inner-sphere nature of the electron-transfer.
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Vrettos JS, Brudvig GW. Water oxidation chemistry of photosystem II. Philos Trans R Soc Lond B Biol Sci 2002; 357:1395-404; discussion 1404-5, 1419-20. [PMID: 12437878 PMCID: PMC1693042 DOI: 10.1098/rstb.2002.1136] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The O(2)-evolving complex of photosystem II catalyses the light-driven four-electron oxidation of water to dioxygen in photosynthesis. In this article, the steps leading to photosynthetic O(2) evolution are discussed. Emphasis is given to the proton-coupled electron-transfer steps involved in oxidation of the manganese cluster by oxidized tyrosine Z (Y(*)(Z)), the function of Ca(2+) and the mechanism by which water is activated for formation of an O-O bond. Based on a consideration of the biophysical studies of photosystem II and inorganic manganese model chemistry, a mechanism for photosynthetic O(2) evolution is presented in which the O-O bond-forming step occurs via nucleophilic attack on an electron-deficient Mn(V)=O species by a calcium-bound water molecule. The proposed mechanism includes specific roles for the tetranuclear manganese cluster, calcium, chloride, Y(Z) and His190 of the D1 polypeptide. Recent studies of the ion selectivity of the calcium site in the O(2)-evolving complex and of a functional inorganic manganese model system that test key aspects of this mechanism are also discussed.
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Affiliation(s)
- John S Vrettos
- Department of Chemistry, Yale University, PO Box 208107, New Haven, CT 06520-8107, USA
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Vrettos JS, Limburg J, Brudvig GW. Mechanism of photosynthetic water oxidation: combining biophysical studies of photosystem II with inorganic model chemistry. BIOCHIMICA ET BIOPHYSICA ACTA 2001; 1503:229-45. [PMID: 11115636 DOI: 10.1016/s0005-2728(00)00214-0] [Citation(s) in RCA: 206] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
A mechanism for photosynthetic water oxidation is proposed based on a structural model of the oxygen-evolving complex (OEC) and its placement into the modeled structure of the D1/D2 core of photosystem II. The structural model of the OEC satisfies many of the geometrical constraints imposed by spectroscopic and biophysical results. The model includes the tetranuclear manganese cluster, calcium, chloride, tyrosine Z, H190, D170, H332 and H337 of the D1 polypeptide and is patterned after the reversible O2-binding diferric site in oxyhemerythrin. The mechanism for water oxidation readily follows from the structural model. Concerted proton-coupled electron transfer in the S2-->S3 and S3-->S4 transitions forms a terminal Mn(V)=O moiety. Nucleophilic attack on this electron-deficient Mn(V)=O by a calcium-bound water molecule results in a Mn(III)-OOH species, similar to the ferric hydroperoxide in oxyhemerythrin. Dioxygen is released in a manner analogous to that in oxyhemerythrin, concomitant with reduction of manganese and protonation of a mu-oxo bridge.
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Affiliation(s)
- J S Vrettos
- Department of Chemistry, Yale University, P.O. Box 208107, New Haven, CT 06520-8107, USA
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11
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Arii H, Nagatomo S, Kitagawa T, Miwa T, Jitsukawa K, Einaga H, Masuda H. A novel diiron complex as a functional model for hemerythrin. J Inorg Biochem 2000; 82:153-62. [PMID: 11132622 DOI: 10.1016/s0162-0134(00)00163-x] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Diiron(II) complexes with a novel dinucleating polypyridine ligand, N,N,N',N'-tetrakis(6-pivalamido-2-pyridylmethyl)-1,3-diaminopropan-2-ol (HTPPDO), were synthesized as functional models of hemerythrin. Structural characterization of the complexes, [Fe2II(Htppdo)(PhCOO)](ClO4)3 (1), [Fe2II(Htppdo)((p-Cl)PhCOO)](ClO4)3 (2), [Fe2II(Htppdo)((p-Cl)PhCOO)](BF4)3 (2') and [Fe2II(tppdo)((p-Cl)PhCOO)](ClO4)2 (3), were accomplished by electronic absorption, and IR spectroscopic, electrochemical, and X-ray diffraction methods. The crystal structures of 1 and 2' revealed that the two iron atoms are asymmetrically coordinated with HTPPDO and bridging benzoate. One of the iron centers (Fe(1)) has a seven-coordinate capped octahedral geometry comprised of an N3O4 donor set which includes the propanol oxygen of HTPPDO. The other iron center (Fe(2)) forms an octahedron with an N3O3 donor set and one vacant site. The two iron atoms are bridged by benzoate (1) or p-chlorobenzoate (2). On the other hand, both Fe atoms of complex 3 are both symmetrically coordinated with N3O4 donors and two bridging ligands; benzoate and the propanolate of TPPDO. Reactions of these complexes with dioxygen were followed by electronic absorption, resonance Raman and ESR spectroscopies. Reversible dioxygen-binding was demonstrated by observation of an intense LMCT band for O2(2-) to Fe(III) at 610 (1) and 606 nm (2) upon exposure of dioxygen to acetone solutions of 1 and 2 prepared under an anaerobic conditions at -50 degrees C. The resonance Raman spectra of the dioxygen adduct of 1 exhibited two peaks assignable to the nu(O-O) stretching mode at 873 and 887 cm(-1), which shifted to 825 and 839 cm(-1) upon binding of (18)O2. ESR spectra of all dioxygen adducts were silent. These findings suggest that dioxygen coordinates to the diiron atoms as a peroxo anion in a mu-1,2 mode. Complex 3 exhibited irreversible dioxygen binding. These results indicate that the reversible binding of dioxygen is governed by the hydrophobicity of the dioxygen-binding environment rather than the iron redox potentials.
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Affiliation(s)
- H Arii
- Department of Applied Chemistry, Faculty of Engineering, Nagoya Institute of Technology, Japan
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12
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Lloyd CR, Raner GM, Moser A, Eyring EM, Ellis WR. Oxymyohemerythrin: discriminating between O2 release and autoxidation. J Inorg Biochem 2000; 81:293-300. [PMID: 11065193 DOI: 10.1016/s0162-0134(00)00093-3] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Myohemerythrin (Mhr) is a non-heme iron O2 carrier (with two irons in the active site) that is typically found in the retractor muscle of marine 'peanut' worms. OxyMhr may either release O2, or undergo an autoxidation reaction in which hydrogen peroxide is released and diferric metMhr is produced. The autoxidation reaction can also be promoted by the addition of certain anions to Mhr solutions. This work, using recombinant Themiste zostericola Mhrs, contrasts the results of environmental effects on these reactions. For the O2 release reaction, deltaVdouble dagger(21.5 degrees C) = +28+/-3 cm3 mol(-1), deltaHdouble dagger(1 atm) = +22+/-1 kcal mol(-1), and deltaSdouble dagger(1 atm) = +28+/-4 eu. The autoxidation reaction (pH 8.0, 21.5 degrees C, 1 atm) displays different kinetic parameters: deltaVdouble dagger = -8+/-2 cm3 mol(-1), deltaHdouble dagger = +24.1+/-0.7 kcal mol(-1), and deltaSdouble dagger = +1+/-1 eu. Autoxidation in the presence of sodium azide is orders of magnitude faster than solvolytic autoxidation. The deltaVdouble dagger parameters for azide anation and azide-assisted autoxidation reaction are +15+/-2 and +59+/-2 cm3 mol(-1), respectively, indicating that the rate-limiting steps for the Mhr autoxidation and anation reactions (including O2 uptake) are not associated with ligand binding to the Fe2 center. The L103V and L103N oxyMhr mutants autoxidize approximately 10(3)-10(5) times faster than the wild-type protein, emphasizing the importance of leucine-103, which may function as a protein 'gate' in stabilizing bound dioxygen.
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Affiliation(s)
- C R Lloyd
- Department of Chemistry, University of Utah, Salt Lake City 84112, USA
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Umakoshi K, Tsuruma Y, Oh CE, Takasawa A, Yasukawa H, Sasaki Y. Synthesis and Redox Properties of Amino Acid-Bridged Dinuclear Iron(III) Complexes. BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 1999. [DOI: 10.1246/bcsj.72.433] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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14
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Brunold TC, Gamelin DR, Stemmler TL, Mandal SK, Armstrong WH, Penner-Hahn JE, Solomon EI. Spectroscopic Studies of Oxidized Manganese Catalase and μ-Oxo-Bridged Dimanganese(III) Model Complexes: Electronic Structure of the Active Site and Its Relation to Catalysis. J Am Chem Soc 1998. [DOI: 10.1021/ja981394l] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Thomas C. Brunold
- Contribution from the Departments of Chemistry, Stanford University, Stanford, California 94305, The University of Michigan, Ann Arbor, Michigan 48109, and Boston College, Chestnut Hill, Massachusetts 02167
| | - Daniel R. Gamelin
- Contribution from the Departments of Chemistry, Stanford University, Stanford, California 94305, The University of Michigan, Ann Arbor, Michigan 48109, and Boston College, Chestnut Hill, Massachusetts 02167
| | - Timothy L. Stemmler
- Contribution from the Departments of Chemistry, Stanford University, Stanford, California 94305, The University of Michigan, Ann Arbor, Michigan 48109, and Boston College, Chestnut Hill, Massachusetts 02167
| | - Sanjay K. Mandal
- Contribution from the Departments of Chemistry, Stanford University, Stanford, California 94305, The University of Michigan, Ann Arbor, Michigan 48109, and Boston College, Chestnut Hill, Massachusetts 02167
| | - William H. Armstrong
- Contribution from the Departments of Chemistry, Stanford University, Stanford, California 94305, The University of Michigan, Ann Arbor, Michigan 48109, and Boston College, Chestnut Hill, Massachusetts 02167
| | - James E. Penner-Hahn
- Contribution from the Departments of Chemistry, Stanford University, Stanford, California 94305, The University of Michigan, Ann Arbor, Michigan 48109, and Boston College, Chestnut Hill, Massachusetts 02167
| | - Edward I. Solomon
- Contribution from the Departments of Chemistry, Stanford University, Stanford, California 94305, The University of Michigan, Ann Arbor, Michigan 48109, and Boston College, Chestnut Hill, Massachusetts 02167
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15
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Sudha C, Mandal SK, Chakravarty AR. Synthesis, X-ray Structures, and Spectroscopic and Electrochemical Properties of (μ-Oxo)bis(μ-carboxylato)diruthenium Complexes Having Six Imidazole Bases as Terminal Ligands. Inorg Chem 1998. [DOI: 10.1021/ic970390z] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Chellamma Sudha
- Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore-560 012, India
| | - Sisir K. Mandal
- Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore-560 012, India
| | - Akhil R. Chakravarty
- Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore-560 012, India
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Paulsen KE, Liu Y, Fox BG, Lipscomb JD, Münck E, Stankovich MT. Oxidation-reduction potentials of the methane monooxygenase hydroxylase component from Methylosinus trichosporium OB3b. Biochemistry 1994; 33:713-22. [PMID: 8292599 DOI: 10.1021/bi00169a013] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Methane monooxygenase (MMO) isolated from Methylosinus trichosporium OB3b consists of hydroxylase (MMOH), reductase (MMOR), and "B" (MMOB) protein components. MMOH contains two oxygen-bridged dinuclear iron clusters that are the sites of O2 activation and hydrocarbon oxidation. Each cluster can be stabilized in diferric [Fe(III).Fc(III)], mixed-valence [Fe(II).Fe(III)], and diferrous [Fe(II).Fe(II)] redox states. We have correlated the EPR spin quantitation of the S = 1/2 mixed-valence state with the system electrode potential to determine both formal redox potential values for MMOH at 4 degrees C: E1 degrees' = +76 +/- 15 mV and E2 degrees' = +21 +/- 15 mV (Em = +48 mV, 61% maximum mixed-valence state). Complementary Mössbauer studies of 57Fe-enriched MMOH allowed all three redox states to be quantitated simultaneously in individual samples and revealed that the distribution of redox states was in accord with the measured potential values. EPR spectra of partially reduced MMOH showed that the apparent midpoint potential values of MMOH-MMOR, MMOH-MMOR-MMOB, and MMOH-MMOR-MMOB-substrate complexes were slightly more positive than that of MMOH alone. In contrast, the MMOH-MMOB complex appeared to have a substantially more negative redox potential. The formal redox potential values of the latter complex were determined to be E1 degrees' = -52 +/- 15 mV and E2 degrees' = -115 +/- 15 mV, respectively, at 4 degrees C (Em = -84 mV, 65% maximum mixed-valence state). This negative 132-mV shift in the midpoint potential of MMOH coupled to MMOB binding suggests that MMOB binds approximately 10(4) more strongly to the diferric state of MMOH than to the diferrous state. Since the potential shift is strongly negative, and since a nearly constant separation between the two formal potential values of MMOH is maintained when MMOB binds, the role of the MMOB-MMOH complex must not be to thermodynamically stabilize the formation of the diferrous cluster which is the form that reacts with O2 during catalysis. However, MMOB binding may provide kinetic stabilization of the diferrous state and/or modulation of the interaction of MMOH with O2 and hydrocarbon substrates. Such roles may be effected through cyclic association and dissociation of the MMOB-MMOH complex as MMOH oscillates between redox states during catalysis, thereby dynamically altering the affinity of this complex.
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Affiliation(s)
- K E Paulsen
- Department of Chemistry, University of Minnesota, Minneapolis 55455
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17
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Zhang BJ, Andrew CR, Tomkinson NP, Sykes AG. Reactivity patterns for redox reactions of monomer forms of myoglobin, hemocyanin and hemerythrin. BIOCHIMICA ET BIOPHYSICA ACTA 1992; 1102:245-52. [PMID: 1390826 DOI: 10.1016/0005-2728(92)90106-c] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Electron-transfer reactions of myoglobin, hemocyanin and hemerythrin with the inorganic complexes [Fe(CN)6]3- (oxidant) and [Co(sep)]2+ (reductant) are considered. Rate constants kFe (25 degrees C) have been determined for the [Fe(CN)6]3- (410 mV) oxidation of horse deoxyMb, I = 0.100 M (NaCl). From the decrease in kFe over the range pH 5.5 to 9.0 a pKa of less than 6.2 is obtained, most likely due to the involvement of the heme propionate(s). At the higher pH values the rate constant is 1.2 x 10(6) M-1 s-1. Rate constants kCo (25 degrees C) for the [Co(sep)]2+ (-260 mV) reduction of metMb are also pH-dependent, pKa = 8.82, corresponding to acid dissociation of the H2O axially coordinated to the Fe(III). The rate constant for the aqua-met form is 2.8 x 10(3) M-1 s-1 at pH values less than 7.0. In contrast, no reaction is observed for the deoxy and met forms of P. interruptus hemocyanin monomer subunit a with the same two complexes (k less than 10(2) M-1 s-1). Comparisons are made with rate constants for hemerythrin, also as the monomer, which have been determined previously. Rate constants for the reactions of deoxy forms with the neutral small molecules, here O2 and H2O2, are also considered. Whereas the reactions of [Fe(CN)6]3- and [Co(sep)]2+ are at the protein surface, those of O2 and H2O2 are at the active site. Hemocyanin with the more buried (approximately 20 A) active site compared with myoglobin (3.8 A) and hemerythrin (6.3 A), does not readily undergo electron transfer with reagents at the surface. However, with the small molecules O2 and H2O2 penetration of the surrounding peptide occurs, with reaction at the active site. Rate constants for the three proteins are now of similar magnitude, and in the range (2.3-7.8) x 10(7) M-1 s-1 for O2, and 10.9 to 3600 M-1 s-1 for H2O2.
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Affiliation(s)
- B J Zhang
- Department of Chemistry, The University, Newcastle upon Tyne, UK
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18
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Zhang BJ, Andrew CR, Tomkinson N, Sykes A. Reactivity patterns for redox reactions of monomer forms of myoglobin, hemocyanin and hemerythrin. ACTA ACUST UNITED AC 1992. [DOI: 10.1016/0167-4838(92)90516-g] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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19
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Long RC, Zhang JH, Kurtz DM, Negri A, Tedeschi G, Bonomi F. Myohemerythrin from the sipunculid, Phascolopsis gouldii: purification, properties and amino acid sequence. BIOCHIMICA ET BIOPHYSICA ACTA 1992; 1122:136-42. [PMID: 1322702 DOI: 10.1016/0167-4838(92)90315-5] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Two previously unknown isoforms, labelled iso I and iso II, of the oxygen-carrying protein, myohemerythrin, have been isolated from carcasses of the sipunculid worm, Phascolopsis gouldii. The two isoforms have non-identical N-terminal amino acid sequences and slightly different absorption spectra in the met form. Far-ultraviolet circular dichroism shows that iso I contains approximately 69% alpha-helix. The complete amino acid sequence for iso I was obtained. The molecular weight calculated from this amino acid sequence and including the active site Fe-O-Fe unit, is 13,829. All of the physical and chemical properties of iso I noted above, including the amino acid sequence, are very similar to those of T. zostericola myohemerythrin. Except for the amino acid sequence, these properties are also very similar to that of a subunit in hemerythrin, the octameric analog found in hemerythrocytes. Only 58 of the 113 residues in P. gouldii hemerythrin are conserved in iso I. Sequence comparisons were used to help identify residues responsible for maintaining the common tertiary and diiron site structures in hemerythrin and myohemerythrin. The seven iron ligand residues previously identified in crystal structures of hemerythrin and myohemerythrin are conserved in iso I. However, none of the ten residue pairs previously identified as engaging in direct salt-bridge or hydrogen bond interactions between subunits in the hemerythrin octamer are conserved in iso I.
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Affiliation(s)
- R C Long
- Department of Chemistry, University of Georgia, Athens 30602
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20
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Wang DL, Holz RC, David SS, Que L, Stankovich MT. Electrochemical properties of the diiron core of uteroferrin and its anion complexes. Biochemistry 1991; 30:8187-94. [PMID: 1868093 DOI: 10.1021/bi00247a014] [Citation(s) in RCA: 55] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The reduction potentials (Em) of the purple acid phosphatase from porcine uterus, uteroferrin (Uf), and its phosphate, arsenate, and molybdate complexes were determined by coulometric methods at various pH values. The midpoint potential of Uf at the pH value for optimal enzyme activity (pH 5) was found to be +367 mV versus a normal hydrogen electrode (NHE), while at pH 6.01 Uf exhibits a reduction potential of +306 mV. At pH 6.01 molybdate was found to shift the potential of Uf more positive by 192 mV, while phosphate and arsenate shift the potential of Uf more negative by 193 and 89 mV, respectively. These shifts are consistent with the different susceptibilities of Uf to aerobic oxidation in the presence of these anions. Comparison of the reduction potential of Uf at pH 7.0 with those reported for other dinuclear non-heme iron enzymes and various (mu-oxo)diiron model complexes suggest that the potential of Uf is too positive to be consistent with a mu-oxo-bridge in Ufo. The pH dependence of the reduction potentials of Uf (60 mV/pH unit) and the fact that the electron transfer rate increases with decreasing pH indicate a concomitant participation of a proton during the oxidation-reduction process. This process was assigned to the protonation of a terminally bound hydroxide ligand at the Fe(II) center upon reduction of Ufo. Structural implications provided by the electrochemical data indicate that molybdate affects the dinuclear core in a manner that differs from that of phosphate and arsenate. This observation is consistent with previous spectroscopic and biochemical studies.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- D L Wang
- Department of Chemistry, University of Minnesota, Minneapolis 55455
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Liu K, Lippard S. Redox properties of the hydroxylase component of methane monooxygenase from Methylococcus capsulatus (Bath). Effects of protein B, reductase, and substrate. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(18)98768-5] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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Abstract
The reactions of hemerythrin from Phascolopsis gouldii with the specific sulfhydryl reagents 5,5'-dithiobis(2-nitrobenzoate), 2,2'-dithiodipyridine, and 4,4'-dithiodipyridine were studied at 25 degrees C. Spectrophotometric measurements showed that 1 mol of disulfide reacted per protein subunit consistent with a single cysteine at residue 50. Reaction leads to dissociation of the octameric structure of the native protein to monomers. The first-order rate constants at 25 degrees C and pH 9.0 for reactions of methemerythrin [(1.5 +/- 0.3) X 10(-3) s-1] and metazidohemerythrin [(4.0 +/- 0.3) X 10(-3) s-1] are independent of both the concentration and the nature of the disulfide. The reactions of methemerythrin are strongly inhibited by ClO4-ion, which however has no effect on the rates of those of metazidohemerythrin. The first-order kinetic behavior is ascribed to a conformational change involving the protein controlling the reaction, and this slow change appears to dominate a number of the reactions of hemerythrin.
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