scholarly journals Nitrogenase of Azotobacter chroococcum. Kinetics of the reduction of oxidized iron-protein by sodium dithionite

1976 ◽  
Vol 155 (1) ◽  
pp. 137-144 ◽  
Author(s):  
R N F Thorneley ◽  
M G Yates ◽  
D J Lowe
Keyword(s):  
Electron Paramagnetic Resonance Spectroscopy ◽  
Sodium Dithionite ◽  
Azotobacter Chroococcum ◽  
High Rate ◽  
Resonance Spectroscopy ◽  
Paramagnetic Resonance ◽  
Fe Protein ◽  
Catalytically Active ◽  
Electron Reduction ◽  
Kinetics Of

The kinetics of the reduction of oxidized Fe-protein of nitrogenase from Azotobacter chroococcum by sodium dithionite were studied by stopped-flow and rapid-freezing e.p.r. (electron-paramagnetic-resonance) spectroscopy. The appearance of the gav. = 1.94 e.p.r. signal (0.24 electron integrated intensity/mol) was associated with a one-electron reduction by SO2- with k greater than 10(8)M-.S-1 at 23 degrees C. A value of k = 1.75s-1 was obtained for the rate of dissociation of S2O42- into 2SO2- at 23 degrees C. Further reductions by SO2- occurred in three slower phases with rate constants in the range 10(4) −10(6)M-1-S-1. These latter phases have no corresponding e.p.r. signal changes and are probably associated with enzymically inactive protein. The high rate of reduction by SO2-of the Fe-protein alone (k greater than 108M1.S-1) relative to the rate of oxidation of the Fe-protein in the catalytically active Fe:Mo-Fe protein complex (k = 2.2 } 102s-1) and the observation that in the steady state the Fe-protein is substantially oxidized means that at normal assay concentrations another reaction must limit the rate of reduction of Fe-protein during turnover.

Characterization of titanium dopants in sodium alanate by electron paramagnetic resonance spectroscopy

2005 ◽  
Vol 20 (12) ◽  
pp. 3265-3269 ◽  
Author(s):  
Meredith T. Kuba ◽  
Sandra S. Eaton ◽  
Christine Morales ◽  
Craig M. Jensen
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Electron Paramagnetic Resonance Spectroscopy ◽  
Epr Spectra ◽  
Minor Amount ◽  
Resonance Spectroscopy ◽  
Paramagnetic Resonance ◽  
Dehydrogenation Kinetics ◽  
Electron Paramagnetic ◽  
Kinetics Of

Electron paramagnetic resonance (EPR) spectra were obtained for samples of Ti-doped NaAlH4 subjected to different numbers of cycles of dehydrogenation/re-hydrogenation. Ti is observed to evolve from its initial Ti(III) state through a series of Ti(0) species during the first 5 cycles. Although the conversion of Ti(III) to Ti(0) occurs much more readily for TiCl3-doped samples than those prepared with TiF3, in both cases the evolution of Ti follows the same sequence that involves 3 distinguishable Ti(0) species and ends in the predominance of the same single Ti(0) species. The spectrum of a sample of NaAlH4 containing 2 mol% of cubic Al3Ti is distinctly different than any of those observed for the Ti(0) species that arise during the hydrogen cycling of the hydride. The major changes in the nature of the predominant Ti species have little if any effect on the dehydrogenation kinetics, which strongly suggests that the profoundly enhanced hydrogen cycling kinetics of Ti-doped NaAlH4 are due to a Ti species present in only a relatively minor amount.

scholarly journals Azotobacter chroococcum 7Fe ferredoxin. Two pH-dependent forms of the reduced 3Fe clusters and its conversion to a 4Fe cluster

1984 ◽  
Vol 224 (1) ◽  
pp. 247-251 ◽  
Author(s):  
S J George ◽  
A J M Richards ◽  
A J Thomson ◽  
M G Yates
Keyword(s):  
Magnetic Circular Dichroism ◽  
Electron Paramagnetic Resonance Spectroscopy ◽  
Iron Chelator ◽  
Anaerobic Treatment ◽  
Azotobacter Chroococcum ◽  
Resonance Spectroscopy ◽  
Paramagnetic Resonance ◽  
High Affinity ◽  
Ph Dependent ◽  
Electron Paramagnetic

Ferredoxin from Azotobacter chroococcum has been studied by low-temperature magnetic-circular-dichroism and electron-paramagnetic-resonance spectroscopy. When aerobically isolated ferredoxin contains a [3Fe-4S] and [4Fe-4S] cluster. Anaerobic treatment with dithionite in the presence of ethanediol reduces the [3Fe-4S] cluster to give two spectroscopically distinct forms RI and RII which are reversibly interconvertible with a pKa approximately 7.5. The higher-pH form, RII, has a high affinity for ferrous ion and converts readily to a [4Fe-4S]1+ cluster, scavenging iron from the medium. The presence of the iron chelator EDTA inhibits this conversion.

scholarly journals Reduction and inactivation of superoxide dismutase by hydrogen peroxide

1974 ◽  
Vol 139 (1) ◽  
pp. 43-48 ◽  
Author(s):  
Robert C. Bray ◽  
Stephen A. Cockle ◽  
E. Martin Fielden ◽  
Peter B. Roberts ◽  
Giuseppe Rotilio ◽  
...  
Keyword(s):  
Superoxide Dismutase ◽  
Prolonged Exposure ◽  
Electron Paramagnetic Resonance Spectroscopy ◽  
Limited Range ◽  
Enzymic Activity ◽  
Resonance Spectroscopy ◽  
Paramagnetic Resonance ◽  
Visible Spectra ◽  
Electron Reduction ◽  
Electron Paramagnetic

Reactions of H2O2 with superoxide dismutase were studied by e.p.r. (electron paramagnetic resonance) spectroscopy and other methods. In agreement with earlier work, the Cu2+ of the enzyme is reduced by H2O2, although the reaction does not go to completion and its kinetics are not simple. With dilute enzyme the time for half-reduction with 9mm-H2O2 is about 150ms. It is suggested that the reaction is a one-electron reduction, involving liberation of O2−. On somewhat more prolonged exposure to H2O2, the enzyme is inactivated. For enzyme in dilute solution and over a limited range of H2O2 concentrations, inactivation is first-order with respect to enzyme and reagent, with k=3.1m−1·s−1 at 20–25°C. Inactivation is accompanied by marked changes in the e.p.r. and visible spectra and appears to be associated with destruction of one histidine residue per subunit. It is suggested that this histidine is close to the metal in the native enzyme and essential for its enzymic activity.

scholarly journals Studies by electron-paramagnetic-resonance spectroscopy of the environment of the metal in the molybdenum cofactor of molybdenum-containing enzymes

1984 ◽  
Vol 222 (3) ◽  
pp. 587-600 ◽  
Author(s):  
T R Hawkes ◽  
R C Bray
Keyword(s):  
Electron Paramagnetic Resonance Spectroscopy ◽  
Gel Filtration ◽  
Sodium Dithionite ◽  
Molybdenum Cofactor ◽  
High Yield ◽  
Cysteine Residues ◽  
Resonance Spectroscopy ◽  
Paramagnetic Resonance ◽  
Organic Part ◽  
Electron Paramagnetic

The molybdenum cofactor prepared by denaturing xanthine oxidase by heat treatment or other methods was partially purified by anaerobic gel filtration in the presence of sodium dithionite, with little loss of activity. A range of products with different elution volumes was obtained. This behaviour is apparently related to association of the molybdenum cofactor with various residual peptides. E.p.r. signals from molybdenum (V) in the active cofactor, present either in crude preparations or in purified fractions, may be generated in dimethyl sulphoxide solution by controlled oxidation carried out on the molybdenum cofactor alone or in the presence of added thiols. The g-values of the spectra suggest that in the oxidized cofactor molybdenum has one terminal oxygen ligand and four ligands from thiolate groups. It is proposed that two of these are from the organic part of the cofactor and two from cysteine residues in the protein or in residual peptides. A signal generated in high yield with little loss of cofactor activity in the presence of thiophenol has g parallel = 2.0258 and g = 1.9793. It is suggested that in this species two cysteine residues have been replaced by two thiophenol molecules. The possible usefulness of the thiophenol complex in further purification of the molybdenum cofactor is discussed.

scholarly journals Iron-sulphur centres in mitochondria from Arum maculatum spadix with very high rates of cyanide-resistant respiration

1977 ◽  
Vol 166 (3) ◽  
pp. 347-355 ◽  
Author(s):  
R Cammack ◽  
J M Palmer
Keyword(s):  
Succinate Dehydrogenase ◽  
Nadh Dehydrogenase ◽  
Electron Paramagnetic Resonance Spectroscopy ◽  
High Rate ◽  
Spin Interaction ◽  
Resonance Spectroscopy ◽  
Paramagnetic Resonance ◽  
Oxidation Reduction ◽  
Fourth Component ◽  
Arum Maculatum

X-band electron-paramagnetic-resonance spectroscopy at 4.2–77K combined with measurements of oxidation-reduction potential was used to identify iron–sulphur centres in Arum maculatum (cuckoo-pint) mitochondria. In the oxidized state a signal with a derivative maximum at g = 2.02 was assigned to succinate dehydrogenase centre S-3. Unreduced particles showed additional signals at g = 2.04 and 1.98 (at 9.2 GHz), which may be due to a spin-spin interaction. In the reduced state a prominent signal at g = 1.93 and 2.02 was resolved into at least three components that could be assigned to centres S-1 and S-2 of succinate dehydrogenase (midpoint potentials −7 and −240 mV respectively at pH 7.2) and a small amount of centre N-1b (e'o= −240 mV) of NADH-ubiquinone reductase. In addition, changes in line shape around −10 mV indicated the presence of a fourth component in this signal. The latter was more readily reduced by NADH than by succinate, suggesting that it might be associated with the external NADH dehydrogenase. The iron-sulphur centres of NADH-ubiquinone reductase were present in an unusually low concentration, indicating that the alternative, non-phosphorylating, NADH dehydrogenase containing a low number of iron-sulphur centres may be responsible for most of the high rate of oxidation of NADH.

scholarly journals The vanadium- and molybdenum-containing nitrogenases of Azotobacter chroococcum. Comparison of mid-point potentials and kinetics of reduction by sodium dithionite of the iron proteins with bound magnesium adenosine 5′-diphosphate

1988 ◽  
Vol 251 (1) ◽  
pp. 165-169 ◽  
Author(s):  
J Bergström ◽  
R R Eady ◽  
R N F Thorneley
Keyword(s):  
Sodium Dithionite ◽  
Azotobacter Chroococcum ◽  
Effective Electron ◽  
Iron Proteins ◽  
Fe Protein ◽  
Protein Components ◽  
Dithionite Ion ◽  
Kinetics Of ◽  
Kinetics Of Reduction

The mid-point potentials of the Fe protein components (Ac2 and Ac2* respectively) of the Mo nitrogenase and V nitrogenase from Azotobacter chroococcum were determined in the presence of MgADP to be −450 mV (NHE) [Ac2(MgADP)2-Ac2*ox.(MgADP)2 couple] and −463 mV (NHE) [Ac2* (MgADP)2-Ac2*ox.(ADP)2 couple] at 23 degrees C at pH 7.2. These values are consistent with a flavodoxin characterized by Deistung & Thorneley [(1986) Biochem. J. 239, 69-75] with Em = −522 mV (NHE) being an effective electron donor to both the Mo nitrogenase and the V nitrogenase in vivo. Ac2*ox.(MgADP)2 and Ac2*ox.(MgADP)2 were reduced by SO2.- (formed by the predissociation of dithionite ion, S2O4(2-)) at similar rates, k = 4.7 × 10(6) +/- 0.5 × 10(6) M-1.s-1 and 3.2 × 10(6) +/- 0.2 × 10(6) M-1.s-1 respectively, indicating structural homology at the electron-transfer site associated with the [4Fe-4S] centre in these proteins.

scholarly journals Structural insights into α-synuclein monomer–fibril interactions

2021 ◽  
Vol 118 (10) ◽  
pp. e2012171118
Author(s):  
Pratibha Kumari ◽  
Dhiman Ghosh ◽  
Agathe Vanas ◽  
Yanick Fleischmann ◽  
Thomas Wiegand ◽  
...  
Keyword(s):  
Amyloid Fibrils ◽  
Electron Paramagnetic Resonance Spectroscopy ◽  
Resonance Spectroscopy ◽  
Local Concentration ◽  
Secondary Nucleation ◽  
Paramagnetic Resonance ◽  
Biophysical Characterization ◽  
Intrinsically Disordered ◽  
Electron Paramagnetic ◽  
Kinetics Of

Protein aggregation into amyloid fibrils is associated with multiple neurodegenerative diseases, including Parkinson’s disease. Kinetic data and biophysical characterization have shown that the secondary nucleation pathway highly accelerates aggregation via the absorption of monomeric protein on the surface of amyloid fibrils. Here, we used NMR and electron paramagnetic resonance spectroscopy to investigate the interaction of monomeric α-synuclein (α-Syn) with its fibrillar form. We demonstrate that α-Syn monomers interact transiently via their positively charged N terminus with the negatively charged flexible C-terminal ends of the fibrils. These intermolecular interactions reduce intramolecular contacts in monomeric α-Syn, yielding further unfolding of the partially collapsed intrinsically disordered states of α-Syn along with a possible increase in the local concentration of soluble α-Syn and alignment of individual monomers on the fibril surface. Our data indicate that intramolecular unfolding critically contributes to the aggregation kinetics of α-Syn during secondary nucleation.

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