scholarly journals An analysis of the reaction kinetics of the hexahaem nitrite reductase of the anaerobic rumen bacterium Wolinella succinogenes

1990 ◽  
Vol 271 (2) ◽  
pp. 457-461 ◽  
Author(s):  
R S Blackmore ◽  
T Brittain ◽  
C Greenwood
Keyword(s):  
Electron Transfer ◽  
Reaction Kinetics ◽  
Nitrite Reductase ◽  
Rate Constants ◽  
Rumen Bacterium ◽  
Square Root ◽  
Wolinella Succinogenes ◽  
Single Turnover ◽  
Internal Electron ◽  
Kinetics Of

The reduction kinetics of both the resting and redox-cycled forms of the nitrite reductase from the anaerobic rumen bacterium Wolinella succinogenes were studied by stopped-flow reaction techniques. Single-turnover reduction of the enzyme by dithionite occurs in two kinetic phases for both forms of the enzyme. When the resting form of the enzyme is subjected to a single-turnover reduction by dithionite, the slower of the two kinetic phases exhibits a hyperbolic dependence of the rate constant on the square root of the reductant concentration, the limiting value of which (approximately 4 s-1) is assigned to a slow internal electron-transfer process. In contrast, when the redox-cycled form of the enzyme is reduced by dithionite in a single-turnover experiment, both kinetic phases exhibit linear dependences of the rate on the square root of dithionite concentration, with associated rate constants of 150 M-1/2.s-1 and 6 M-1/2.s-1. Computer simulations of both the reduction processes shows that no unique set of rate constants can account for the kinetics of both forms, although the kinetics of the redox-cycled species is consistent with a much enhanced rate of internal electron transfer. Under turnover conditions the time course for reduction of the enzyme, in the presence of millimolar levels of nitrite and 100 mM-dithionite, is extremely complex. A working model for the mechanism of the turnover activity of the enzyme is proposed which very closely describes the reaction kinetics over a wide range of substrate concentrations, as shown by computer simulation. The similarity in the action of the nitrite reductase enzyme and mammalian cytochrome c oxidase is commented upon.

scholarly journals Storage, transport, release: heme versatility in nitrite reductase electron transfer studied by molecular dynamics simulations

2015 ◽  
Vol 17 (6) ◽  
pp. 4483-4491 ◽  
Author(s):  
Anna Bauß ◽  
Thorsten Koslowski
Keyword(s):  
Molecular Dynamics ◽  
Electron Transfer ◽  
Molecular Dynamics Simulations ◽  
Campylobacter Jejuni ◽  
Nitrite Reductase ◽  
Thermodynamic Integration ◽  
Wolinella Succinogenes ◽  
Dynamics Simulations ◽  
Kinetics Of

Using molecular dynamics simulations of the thermodynamic integration type, we study the energetics and kinetics of electron transfer through the nitrite reductase enzyme of Sulfurospirillum deleyianum, Wolinella succinogenes and Campylobacter jejuni.

scholarly journals The effects of the chemical environment of menaquinones in lipid monolayers on mercury electrodes on the thermodynamics and kinetics of their electrochemistry

2021 ◽  
Author(s):  
Karuppasamy Dharmaraj ◽  
Dirk Dattler ◽  
Heike Kahlert ◽  
Uwe Lendeckel ◽  
Felix Nagel ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Rate Constants ◽  
Transfer Rate ◽  
Chemical Environment ◽  
Lipid Monolayers ◽  
Redox Potentials ◽  
Electron Transfer Rate ◽  
Thermodynamics And Kinetics ◽  
Mercury Electrodes ◽  
Kinetics Of

AbstractThe effects of the chemical environment of menaquinones (all-trans MK-4 and all-trans MK-7) incorporated in lipid monolayers on mercury electrodes have been studied with respect to the thermodynamics and kinetics of their electrochemistry. The chemical environment relates to the composition of lipid films as well as the adjacent aqueous phase. It could be shown that the addition of all-trans MK-4 to TMCL does not change the phase transition temperatures of TMCL. In case of DMPC monolayers, the presence of cholesterol has no effect on the thermodynamics (formal redox potentials) of all-trans MK-7, but the kinetics are affected. Addition of an inert electrolyte (sodium perchlorate; change of ionic strength) to the aqueous phase shifts the redox potentials of all-trans MK-7 only slightly. The formal redox potentials of all-trans MK-4 were determined in TMCL and nCL monolayers and found to be higher in nCL monolayers than in TMCL monolayers. The apparent electron transfer rate constants, transfer coefficients and activation energies of all-trans MK-4 in cardiolipins have been also determined. Most surprisingly, the apparent electron transfer rate constants of all-trans MK-4 exhibit an opposite pH dependence for TMCL and nCL films: the rate constants increase in TMCL films with increasing pH, but in nCL films they increase with decreasing pH. This study is a contribution to understand environmental effects on the redox properties of membrane bond redox systems. Graphical abstract

Electrode kinetics of Eu3+/Eu2+ reaction by cyclic voltammetry

1982 ◽  
Vol 47 (7) ◽  
pp. 1773-1779 ◽  
Author(s):  
T. P. Radhakrishnan ◽  
A. K. Sundaram
Keyword(s):  
Electron Transfer ◽  
Rate Constants ◽  
Outer Sphere ◽  
Electrode Reaction ◽  
Transfer Reactions ◽  
Cyclic Voltammetric ◽  
Edta Solution ◽  
Kinetics Of ◽  
Activated Complex ◽  
Good Agreement

The paper is a detailed study of the cyclic voltammetric behaviour of Eu3+ at HMDE in molar solutions of KCl, KBr, KI, KSCN and in 0.1M-EDTA solution with an indigenously built equipment. The computed values of the rate constants at various scan rates show good agreement with those reported by other electrochemical methods. In addition, the results indicate participation of a bridged activated complex in the electron-transfer step, the rate constants showing the trend SCN- > I- > Br- > Cl- usually observed for bridging order of these anions in homogeneous electron-transfer reactions. The results for Eu-EDTA system, however, indicate involvement of an outer sphere activated complex in the electrode reaction.

Modulation spectroscopy. Kinetics for the self-reactions of some α-aminoalkyl radicals in solution

1982 ◽  
Vol 60 (3) ◽  
pp. 274-278 ◽  
Author(s):  
Paul R. Marriott ◽  
Arlindo L. Castelhano ◽  
David Griller
Keyword(s):  
Absorption Spectrum ◽  
Reaction Kinetics ◽  
Unpaired Electron ◽  
Rate Constants ◽  
Lone Pair ◽  
The Self ◽  
Modulation Spectroscopy ◽  
Alkyl Radicals ◽  
Diffusion Controlled ◽  
Kinetics Of

The optical spectra and reaction kinetics of some a-aminoalkyl radicals, RĊHN(CH2R)2; R≡H, Me, Ph, were measured in solution using the technique of modulation spectroscopy. These radicals undergo diffusion controlled self-reaction with rate constants [Formula: see text]. When R≡Ph, the absorption spectrum has a well defined maximum at 346 nm; ε = 3390 M−1 cm−1, while the spectra when R≡H or Me were less intense [Formula: see text] and tailed into the visible. These spectra are substantially red-shifted when compared with those of simple alkyl radicals, an effect which is thought to be due to the interaction between the unpaired electron and the lone pair of electrons on nitrogen.

scholarly journals Some electron-transfer reactions involving carbodi-imide-modified cytochrome c

1987 ◽  
Vol 243 (2) ◽  
pp. 379-384 ◽  
Author(s):  
A J Mathews ◽  
T Brittain
Keyword(s):  
Electron Transfer ◽  
Ionic Strength ◽  
Protein Charge ◽  
Native Proteins ◽  
Wide Range ◽  
Internal Electron ◽  
Modified Proteins ◽  
Time Courses ◽  
Low Ionic Strength ◽  
Kinetics Of

The reaction kinetics of native and carbodi-imide-modified tuna and horse heart cytochromes c with both a strong (dithionite) and a relatively weak (ascorbate) reducing agent were studied over a wide range of conditions. In their reactions with dithionite both the native and modified cytochromes exhibit single exponential time courses. The effects of dithionite concentration and ionic strength on the rate of the reduction are complex and can best be explained in terms of the model proposed by Lambeth & Palmer [(1973) J. Biol. Chem. 248, 6095-6103]. According to this model, at low ionic strength the native proteins are reduced almost exclusively by S2O4(2-) whereas the modified proteins showed reactivity towards both S2O4(2-) and SO2.-. These findings are interpreted in terms of the different charge characteristics of the carbodi-imide-modified proteins relative to the native proteins. The findings that the modified proteins react with ascorbate in a biphasic manner are explained as arising from ascorbate binding to a reducible form of the protein, before electron transfer, with an equilibrium between the ascorbate-reducible form of the protein and a non-reducible form. Estimates were obtained for both the ascorbate equilibrium binding constant and the rate constant for the internal electron transfer for both the native and modified horse and tuna proteins. The effect of pH on the reactions indicates that the active reductant in all cases is ascorbate2-. The studies of ascorbate reactivity yield important information concerning the proposed correlation between ascorbate reducibility and the presence of a 695 nm-absorption band, and the study of dithionite reactivity illustrates the effect of protein charge and solution ionic strength on the relative contributions made by the species SO2.- and S2O4(2-) to the reduction of ferricytochrome c.

KINETICS OF THE OXIDATION OF URANIUM (IV) BY IRON (III) IN AQUEOUS SOLUTIONS OF PERCHLORIC ACID

1955 ◽  
Vol 33 (12) ◽  
pp. 1780-1791 ◽  
Author(s):  
R. H. Betts
Keyword(s):  
Electron Transfer ◽  
Ionic Strength ◽  
Aqueous Solutions ◽  
Perchloric Acid ◽  
Rate Constants ◽  
Kcal Mole ◽  
Kinetics Of Oxidation ◽  
Temperature Coefficients ◽  
Kinetics Of ◽  
Rate Controlling Step

The kinetics of oxidation of uranium (IV) by iron (III) in aqueous solutions of perchloric acid have been investigated at four temperatures between 3.1 °C. and 24.8 °C. The reaction was followed by measurement of the amount of ferrous ion formed. For the conditions (H+) = 0.1–1.0 M, ionic strength = 1.02, (FeIII) = 10−4–10−5 M, and (UIV) = 10−4–10−5 M, the observed rate law is d(Fe2+)/dt = −2d(UIV)/dt[Formula: see text]K1 and K2 are the first hydrolysis constants for Fe3+ and U4+, respectively, and K′ and K″ are pseudo rate constants. At 24.8 °C., K′ = 2.98 sec.−1, and K″ = 10.6 mole liter−1 sec−1. The corresponding temperature coefficients are ΔH′ = 22.5 kcal./mole and ΔH″ = 24.2 kcal./mole. The kinetics of the process are consistent with a mechanism which involves, as a rate-controlling step, electron transfer between hydrolyzed ions.

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