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.

scholarly journals Nonenzymatic NADH-Dependent Reduction of Keggin-Type 12-Tungstocobaltate(III) in Aqueous Medium

2011 ◽  
Vol 8 (3) ◽  
pp. 1152-1157
Author(s):  
Prabla Kumari ◽  
Alaka Das ◽  
Dillip Kumar Baral ◽  
A. K. Pattanaik ◽  
P. Mohanty
Keyword(s):  
Electron Transfer ◽  
Transition State ◽  
Aqueous Medium ◽  
Transfer Reaction ◽  
Activation Parameters ◽  
Electron Transfer Reaction ◽  
Transfer Reactions ◽  
Electron Transfer Reactions ◽  
First Order ◽  
Kinetics Of

The kinetics of the electron transfer reaction of NADH with 12-tungstocobaltate(III) has been studied over the range 5.07 ≤ 104[NADH] ≤ 15.22 mol dm-3, 7.0 ≤ pH ≤ 8.0 and 20 ≤ t ≤ 35oC in aqueous medium. The electron transfer reaction showed first-order dependence each in [NADH]Tand [12-tungstocobaltate(III)]T. The products of the reaction were found to be NAD+and 12-tungstocobaltate(II). The activation parameters ΔH#(kJ mol-1) and ΔS#(JK-1mol-1) of the electron transfer reactions were found to be 64.4±1.8 and -48.86±6.0. Negative value of ΔS#is an indicative of an ordered transition state for the electron transfer reaction.

scholarly journals Kinetics of nitrogenase of Klebsiella pneumoniae. Heterotropic interactions between magnesium-adenosine 5′-diphosphate and magnesium-adenosine 5′-triphosphate

1977 ◽  
Vol 165 (2) ◽  
pp. 255-262 ◽  
Author(s):  
R N F Thorneley ◽  
A Cornish-Bowden
Keyword(s):  
Electron Transfer ◽  
Steady State ◽  
Protein A ◽  
Competitive Inhibitor ◽  
Electron Transfer Reaction ◽  
H2 Evolution ◽  
Fe Protein ◽  
Steady State Kinetics ◽  
Steady State Kinetic ◽  
Kinetics Of

The effects of MgADP and MgATP on the kinetics of a pre-steady-state electron-transfer reaction and on the steady-state kinetics of H2 evulution for nitrogenase proteins of K. pneumoniae were studied. MgADP was a competitive inhibitor of MgATP in the MgATP-induced electron transfer from the Fe-protein to the Mo-Fe-protein. A dissociation constant K′i = 20 micron was determined for MgADP. The release of MgADP or a coupled conformation change in the Fe-protein of K.pneumoniae occurred with a rate comparable with that of electron transfer, k approximately 2 × 10(2)S-1. Neither homotropic nor heterotropic interactions involving MgATP and MgADP were observed for this reaction. Steady-state kinetic data for H2 evolution exhibited heterotropic effects between MgADP and MgATP. The data have been fitted to symmetry and sequential-type models involving conformation changes in two identical subunits. The data suggest that the enzyme can bind up to molecules of either MgATP or MgADP, but is unable to bind both nucleotides simultaneously. The control of H2 evolution by the MgATP/MgADP ratio is not at the level of electron transfer between the Fe- and Mo-Fe-proteins.

scholarly journals Non enzymatic NADH-dependent reduction of Cis-[Co(en)2(H2O)2]3+ in aqueous medium

2018 ◽  
Vol 6 (2) ◽  
pp. 163
Author(s):  
Bharati Behera ◽  
Jashoda Behera
Keyword(s):  
Electron Transfer ◽  
Aqueous Medium ◽  
Transfer Reaction ◽  
Activation Parameters ◽  
Electron Transfer Reaction ◽  
Transfer Reactions ◽  
Electron Transfer Reactions ◽  
First Order ◽  
Order Dependence ◽  
Kinetics Of

The kinetics of the electron transfer reaction of NADH with Cis-[Co(en)2(H2O)2]3+ has been studied over the range 1.0 ≤ 102 [NADH] ≤ 3.0 mol dm-3, 7.0 ≤ pH ≤ 8.0 and 200C ≤ t ≤ 350C in aqueous medium. The rate of electron transfer reaction was found to be first-order dependence each in [NADH]T and Cis-[Co(en)2(H2O)2]3+T. The products of the reaction were found to be NAD+ and Co(II). The corresponding activation parameters of the electron transfer reactions were found to be as ΔH#=27.55 kJ mol-1 and  ΔS#= -189.35 JK-1mol-1. 

Kinetics of Electron Transfer Reaction between Co(II) and Chlorate Ions: Experimental and Modeling Study

2021 ◽  
Vol 43 (5) ◽  
pp. 559-559
Author(s):  
Mahwish Mobeen Khan and Syed Mumtaz Danish Naqvi Mahwish Mobeen Khan and Syed Mumtaz Danish Naqvi
Keyword(s):  
Electron Transfer ◽  
Transfer Reaction ◽  
High Energy ◽  
Electron Transfer Reaction ◽  
Maximum Likelihood Estimates ◽  
Oxidation Catalyst ◽  
Standard Entropy ◽  
Rate Of Reaction ◽  
Kinetics Of ◽  
Activated Complex

This research article reports original experimental and modeling detail of kinetics of the electron transfer reaction between Co(II) and chlorate ions in acetic acid solution. Design of experiment methodology has been employed to elucidate the effects of temperature and initial concentrations of reactants on the rate of reaction. Levenberg-Marquardt method has been used to fit processed kinetic data (temperatures, initial concentrations of reactants, and concentrations and rates of production of Co(III)) on to various possible rate equations. This algorithm provides a proficient mean for compensating the capricious effects of the experimental process variables and results in the maximum likelihood estimates of the kinetic parameters. The most significant rate law has been selected, on the basis of statistical analyses of the residuals between the predicted and experimental rates. The analyses suggest that the intrinsic rate of reaction is proportional to first power of chlorate concentration but for Co(II) the order is fractional (0.7455 ≈ and#190;). The effect of temperature on the observed rate constant (precision = 0.02 %) is excellently described by the Arrhenius and Eyring equations and the sluggish nature of the reaction is clearly manifested by the high energy (andgt; 93 kJ/mol), negative entropy (-28.5286 J/mol-K) and very small equilibrium constant of activation. Further fairly negative standard entropy of activation shows there is usually considerable rearrangement of energy among various degrees of freedom during the formation of activated complex and proposes an associative mechanism for formation of the activated complex. This research is performed to develop a kinetic model for the electron transfer reaction between Co(II) and chlorate ion. As a result, a redox couple of Co(II)/Co(III) has been formed which is used as a potent oxidation catalyst in chemical industries.

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