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 Nitrogenase of Klebsiella pneumoniae. Kinetic studies on the Fe protein involving reduction by sodium dithionite, the binding of MgADP and a conformation change that alters the reactivity of the 4Fe-4S centre

1987 ◽  
Vol 246 (2) ◽  
pp. 455-465 ◽  
Author(s):  
G A Ashby ◽  
R N F Thorneley
Keyword(s):  
Klebsiella Pneumoniae ◽  
Rate Constants ◽  
Protein Conformation ◽  
Kinetic Studies ◽  
Sodium Dithionite ◽  
Conformation Change ◽  
Fe Protein ◽  
Redox Active ◽  
Dithionite Ion ◽  
Kinetics Of

The kinetics of reduction of indigocarmine-dye-oxidized Fe protein of nitrogenase from Klebsiella pneumoniae (Kp2ox) by sodium dithionite in the presence and absence of MgADP were studied by stopped-flow spectrophotometry at 23 degrees C and at pH 7.4. Highly co-operative binding of 2MgADP (composite K greater than 4 × 10(10) M-2) to Kp2ox induced a rapid conformation change which caused the redox-active 4Fe-4S centre to be reduced by SO2-.(formed by the predissociation of dithionite ion) with k = 3 × 10(6) M-1.s-1. This rate constant is at least 30 times lower than that for the reduction of free Kp2ox (k greater than 10(8) M-1.s-1). Two mechanisms have been considered and limits obtained for the rate constants for MgADP binding/dissociation and a protein conformation change. Both mechanisms give rate constants (e.g. MgADP binding 3 × 10(5) less than k less than 3 × 10(6) M-1.s-1 and protein conformation change 6 × 10(2) less than k less than 6 × 10(3) s-1) that are similar to those reported for creatine kinase (EC 2.7.3.2). The kinetics also show that in the catalytic cycle of nitrogenase with sodium dithionite as reductant replacement of 2MgADP by 2MgATP occurs on reduced and not oxidized Kp2. Although the Kp2ox was reduced stoichiometrically by SO2-. and bound two equivalents of MgADP with complete conversion into the less-reactive conformation, it was only 45% active with respect to its ability to effect MgATP-dependent electron transfer to the MoFe protein.

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.

scholarly journals Vanadium nitrogenase of Azotobacter chroococcum. MgATP-dependent electron transfer within the protein complex

1989 ◽  
Vol 257 (3) ◽  
pp. 789-794 ◽  
Author(s):  
R N F Thorneley ◽  
N H J Bergström ◽  
R R Eady ◽  
D J Lowe
Keyword(s):  
Electron Transfer ◽  
Transfer Reaction ◽  
Competitive Inhibitor ◽  
Electron Transfer Reaction ◽  
Azotobacter Chroococcum ◽  
First Order ◽  
Fe Protein ◽  
Vanadium Nitrogenase ◽  
Electron Transfer Complex ◽  
Kinetics Of

The kinetics of MgATP-induced electron transfer from the Fe protein (Ac2V) to the VFe protein (AclV) of the vanadium-containing nitrogenase from Azotobacter chroococcum were studied by stopped-flow spectrophotometry at 23 degrees C at pH 7.2. They are very similar to those of the molybdenum nitrogenase of Klebsiella pneumoniae [Thorneley (1975) Biochem. J. 145, 391-396]. Extrapolation of the dependence of kobs. on [MgATP] to infinite MgATP concentration gave k = 46 s-1 for the first-order electron-transfer reaction that occurs with the Ac2V MgATPAclV complex. MgATP binds with an apparent KD = 230 +/- 10 microM and MgADP acts as a competitive inhibitor with Ki = 30 +/- 5 microM. The Fe protein and VFe protein associate with k greater than or equal to 3 x 10(7) M-1.s-1. A comparison of the dependences of kobs. for electron transfer on protein concentrations for the vanadium nitrogenase from A. chroococcum with those for the molybdenum nitrogenase from K. pneumoniae [Lowe & Thorneley (1984) Biochem. J. 224, 895-901] indicates that the proteins of the vanadium nitrogenase system form a weaker electron-transfer complex.

Kinetics of reduction of eight viologens by dithionite ion

1985 ◽  
Vol 107 (9) ◽  
pp. 2632-2635 ◽  
Author(s):  
K. Tsukahara ◽  
R. G. Wilkins
Keyword(s):  
Dithionite Ion ◽  
Kinetics Of ◽  
Kinetics Of Reduction

Rate of reaction of dithionite ion with oxygen in aqueous solution

1964 ◽  
Vol 19 (3) ◽  
pp. 522-525 ◽  
Author(s):  
J. A. Morello ◽  
Margot R. Craw ◽  
H. P. Constantine ◽  
R. E. Forster
Keyword(s):  
Aqueous Solution ◽  
Reaction Rate ◽  
Initial Rate ◽  
Sodium Dithionite ◽  
Zero Order ◽  
Flowing Liquid ◽  
First Order ◽  
Rate Of Reaction ◽  
Dithionite Ion ◽  
Kinetics Of

The rate of removal of oxygen from aqueous solution by sodium dithionite in 0.1 m sodium hydroxide was studied in a rapid-reaction apparatus using a membrane-covered polarographic cell to determine Po2 in the flowing liquid. The measurements were made at 37 C, so that the data would be applicable in studies of the kinetics of oxyhemoglobin in blood. The initial concentrations in the mixed reacting solution were between 8 x 10-5 m and 47.5 x 10-5 m for dithionite, and either 10 x 10-5 m or 47.8 x 10-5 m for O2. The reaction over the first 40 msec was found to be first order with respect to dithionite and zero order with respect to molecular oxygen. The initial rate constant was 42.5 ± sd 3.6 sec-1. oxygen reduction by dithionite; hemoglobin; deoxygenation rate; dithionite-oxygen reaction rate Submitted on June 17, 1963

Effect of pH and inhibitors on beta-amyloid fibril assembly

1996 ◽  
Vol 54 ◽  
pp. 752-753
Author(s):  
Beverly E. Maleeff ◽  
Timothy K. Hart ◽  
Stephen J. Wood ◽  
Ronald Wetzel
Keyword(s):  
Amyloid Fibril ◽  
Peptide Fragment ◽  
Hydrophobic Peptides ◽  
Amyloid Fibril Formation ◽  
Effects Of Ph ◽  
Severity Of The Disease ◽  
Kinetics Of ◽  
The Brain

Alzheimer's disease is characterized post-mortem in part by abnormal extracellular neuritic plaques found in brain tissue. There appears to be a correlation between the severity of Alzheimer's dementia in vivo and the number of plaques found in particular areas of the brain. These plaques are known to be the deposition sites of fibrils of the protein β-amyloid. It is thought that if the assembly of these plaques could be inhibited, the severity of the disease would be decreased. The peptide fragment Aβ, a precursor of the p-amyloid protein, has a 40 amino acid sequence, and has been shown to be toxic to neuronal cells in culture after an aging process of several days. This toxicity corresponds to the kinetics of in vitro amyloid fibril formation. In this study, we report the biochemical and ultrastructural effects of pH and the inhibitory agent hexadecyl-N-methylpiperidinium (HMP) bromide, one of a class of ionic micellar detergents known to be capable of solubilizing hydrophobic peptides, on the in vitro assembly of the peptide fragment Aβ.

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