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 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 The mechanism of Klebsiella pneumoniae nitrogenase action. The determination of rate constants required for the simulation of the kinetics of N2 reduction and H2 evolution

1984 ◽  
Vol 224 (3) ◽  
pp. 895-901 ◽  
Author(s):  
D J Lowe ◽  
R N F Thorneley
Keyword(s):  
Klebsiella Pneumoniae ◽  
Rate Constants ◽  
Competitive Inhibitor ◽  
H2 Evolution ◽  
Protein Ratio ◽  
Mofe Protein ◽  
Fe Protein ◽  
Mutual Displacement ◽  
Kinetics Of

Kinetic data for Klebsiella pneumoniae nitrogenase were used to determine the values of nine of the 17 rate constants that define the scheme for nitrogenase action described by Lowe & Thorneley [(1984) Biochem. J. 224, 877-886]. Stopped-flow spectrophotometric monitoring of the MgATP-induced oxidation of the Fe protein (Kp2) by the MoFe protein (Kp1) was used to determine the rates of association (k+1) and dissociation (k-1) of reduced Kp2(MgATP)2 with Kp1. The dependences of the apparent KNm2 on Fe protein/MoFe protein ratio and H2 partial pressure were used to determine the mutual displacement rates of N2 and H2 (k+10, k-10, k+11 and k-11). These data also allowed the rate constants for H2 evolution from progressively more reduced forms of Kp1 to be determined (k+7, k+8 and k+9). A mechanism for N2-dependent catalysis of 1H2H formation from 2H2 that requires H2 to be a competitive inhibitor of N2 reduction is also presented.

Kinetics of the Ozonation of Tetrabromobisphenol-A in Wastewater

2011 ◽  
Vol 383-390 ◽  
pp. 2945-2950 ◽  
Author(s):  
Jie Zhang ◽  
Shi Long He ◽  
Mei Feng Hou ◽  
Li Ping Wang ◽  
Li Jiang Tian
Keyword(s):  
Rate Constants ◽  
Apparent Rate Constant ◽  
Reaction Rate ◽  
Batch Reactor ◽  
Kinetic Studies ◽  
Tetrabromobisphenol A ◽  
First Order ◽  
Reaction Rate Constants ◽  
Pseudo First Order ◽  
Kinetics Of

The kinetics of TBBPA degradation by ozonation in semi-batch reactor was studied. The reaction rate constants of TBBPA with O3 and •OH were measured by means of direct ozone attack and competition kinetics, and the values of which were 6.10 l/(mol•s), 4.8×109 l/(mol•s), respectively. Results of kinetic studies showed that TBBPA degradation by ozonation under the different conditions tested followed the pseudo-first-order. The values of apparent rate constant of TBBPA degradation increased with the increase of ozone dosage and pH, but decreased with the increase of initial TBBPA concentration.

KINETIC STUDIES OF METHYL-BIS-β-CHLOROETHYLAMINE: III. THE KINETICS OF THE DIMERIZATION IN METHANOL

1948 ◽  
Vol 26b (2) ◽  
pp. 175-180 ◽  
Author(s):  
C. A. Winkler ◽  
A. W. Hay ◽  
A. L. Thompson
Keyword(s):  
Rate Constants ◽  
Initial Rate ◽  
Kinetic Studies ◽  
First Order ◽  
Rate Expression ◽  
Principal Reaction ◽  
Kinetics Of ◽  
Rate Controlling Step

The principal reaction of methyl-bis-β-chloroethylamine in methanol is dimerization, which results in one chlorine from each molecule becoming ionic, but this is accompanied by slight alcoholysis. The rate-controlling step is believed to be the first order formation of an ethylenimonium ion which reacts rapidly with one of its kind to form dimer. The rate expression as calculated from initial rate constants is k (initial) = 4.0 × 1013e−19600/RThr.−1.

scholarly journals Nitrogenase of Klebsiella pneumoniae: kinetics of formation of the transition-state complex and evidence for an altered conformation of MoFe protein lacking a FeMoco centre

1997 ◽  
Vol 326 (3) ◽  
pp. 637-640 ◽  
Author(s):  
Faridoon K. YOUSAFZAI ◽  
Robert R. EADY
Keyword(s):  
Klebsiella Pneumoniae ◽  
Transition State ◽  
Nitrogenase Activity ◽  
Active Species ◽  
Slow Phase ◽  
Mofe Protein ◽  
Fe Protein ◽  
Catalytically Active ◽  
Mo Content ◽  
Kinetics Of

We have investigated the kinetics of inactivation of Mo-nitrogenase isolated from Klebsiella pneumoniae when it forms an inhibited putative transition-state complex on incubation with ADP and AlF4-. In the presence of excess Kp2 (Fe protein of the Mo-nitrogenase of K. pneumoniae), the kinetics were found to depend on the Mo content of Kp1 (the MoFe protein of Mo-nitrogenase of K. pneumoniae). The residual nitrogenase activity versus time of incubation using Kp1 preparations containing integral, i.e. one or two Mo atoms per molecule of Kp1, were essentially monophasic, but significantly different rates of inactivation were observed. In contrast, the progress curves for preparations of Kp1 with non-integral Mo content were biphasic, suggesting the presence of two discrete catalytically active species of Kp1. The best fit to the observed data was obtained with a two-exponential expression, the amplitude of which was consistent with the Mo content, provided that the fast phase of the reaction was assigned to a Kp1 species containing one, and the slow phase to a species containing two Mo atoms per α2β2 tetramer. This analysis provides the first evidence for the existence of a catalytically active Kp1 species containing a single Mo atom. These data also indicate that MoFe protein which does not have all FeMoco binding sites occupied has an altered conformation compared with a fully loaded protein, and that the Fe protein reacts with these conformations at different rates to form the stable, but inhibited transition-state complex.

scholarly journals THE PHOTOINITIATED ADDITION OF MERCAPTANS TO OLEFINS: III. THE KINETICS OF THE ADDITION OF THIOPHENOL TO STYRENE AND TO 1-OCTENE

1957 ◽  
Vol 35 (7) ◽  
pp. 723-733 ◽  
Author(s):  
R. H. Pallen ◽  
C. Sivertz
Keyword(s):  
Free Radical ◽  
Rate Constants ◽  
Chain Transfer ◽  
Kinetic Studies ◽  
Activation Energies ◽  
Reverse Reaction ◽  
Kinetics Of

Kinetic studies were made of the free radical photoinitiated addition of thiophenol to 1-octene and to styrene in the absence of oxygen. In addition to the usual attack, chain transfer, and termination steps, it is found that a reverse reaction accompanies the attack step, [Formula: see text] The rate constants for the thiophenol–styrene reaction were calculated to be [Formula: see text]kt = 2 × 107 liters.moles−1sec.−1. The over-all activation energies for the two reactions were found to be E (1-octene) = 1.2 kcal., E (styrene) = 2.4 kcal.; suggestions are submitted as to why these activation energies are so low. These reactions are compared with n-butyl mercaptan – olefin reactions.

KINETIC STUDIES OF PROTEIN–DYE AND ANTIBODY–HAPTEN INTERACTIONS WITH THE TEMPERATURE-JUMP METHOD

1962 ◽  
Vol 40 (9) ◽  
pp. 1786-1797 ◽  
Author(s):  
A. Froese ◽  
A. H. Sehon ◽  
M. Eigen
Keyword(s):  
Relaxation Time ◽  
Bovine Serum Albumin ◽  
Rate Constants ◽  
Temperature Jump ◽  
Relaxation Times ◽  
Kinetic Studies ◽  
Single Relaxation Time ◽  
Effects Of Temperature ◽  
Arsonic Acid ◽  
Kinetics Of

The kinetics of protein–dye and antibody–hapten reactions were studied with the temperature-jump method. The systems used consisted of (i) bovine serum albumin (BSA) and the dye 1-naphthol-4-[4-(4′-azobenzene azo)phenyl arsonic acid], referred to as N—R′, (ii) BSA and the dye 1-naphthol-2-sulphonic acid-4-[4-(4′-azobenzene azo)phenyl arsonic acid], referred to as NS—R′, and (iii) rabbit antibodies to phenyl arsonic acid [Ab] and the hapten N—R′.Each of the systems exhibited a single relaxation time. From the analysis of the concentration dependence of the relaxation times, it was concluded that each system could be represented by the reactions[Formula: see text]where P refers to BSA or Ab, and D to N—R′ or NS—R′. The following rate constants were calculated for the three systems at 25 °C:[Formula: see text]The effects of temperature and pH on the rate constants of the system BSA – N—R′ are discussed.

scholarly journals Klebsiella pneumoniae nitrogenase. The pre-steady-state kinetics of MoFe-protein reduction and hydrogen evolution under conditions of limiting electron flux show that the rates of association with the Fe-protein and electron transfer are independent of the oxidation level of the MoFe-protein

1991 ◽  
Vol 279 (1) ◽  
pp. 81-85 ◽  
Author(s):  
K Fisher ◽  
D J Lowe ◽  
R N F Thorneley
Keyword(s):  
Electron Transfer ◽  
Steady State ◽  
Klebsiella Pneumoniae ◽  
Electron Flux ◽  
High Electron ◽  
H2 Evolution ◽  
Mofe Protein ◽  
Fe Protein ◽  
Steady State Kinetics ◽  
Kinetics Of

The pre-steady-state kinetics of H2 evolution from Klebsiella pneumoniae nitrogenase functioning at 23 degrees C, pH 7.4, under conditions of extremely low electron flux through the MoFe-protein exhibited a lag phase of several minutes duration. The approach to a steady-state rate of H2 evolution was accompanied by a 50% decrease in the amplitude of the MoFe-protein e.p.r. signal. These kinetics have been simulated using our published kinetic model for nitrogenase [Lowe & Thorneley (1984) Biochem. J. 224, 877-886], which was developed using data obtained with nitrogenase functioning at high electron fluxes. The e.p.r. data showed that the rate of complex-formation between reduced Fe-protein and the MoFe-protein (k+1 = 5 x 10(7) M-1.s-1) is the same for the resting (E0) and one-electron-reduced (E1H) states of the MoFe-protein. Stopped-flow spectrophotometry also showed that electron transfer from the Fe-protein to the MoFe-protein in states E0 and E1H occurs at the same rate (kobs. = 140 s-1). These data support our previous assumption that the rate constants that define the ‘Fe-protein cycle’ are independent of the level of reduction of the MoFe-protein.

scholarly journals Aquation reaction of iminodiacetate complex of oxidovanadium(IV) with 2,2’-bipyridine induced by Fe(III) ions: Kinetic studies

2019 ◽  
Vol 44 (4) ◽  
pp. 300-306
Author(s):  
Joanna Drzeżdżon ◽  
Agnieszka Piotrowska-Kirschling ◽  
Lech Chmurzyński ◽  
Dagmara Jacewicz
Keyword(s):  
Aqueous Solutions ◽  
Computer Program ◽  
Rate Constants ◽  
Reaction Rate ◽  
Kinetic Studies ◽  
Reaction Rate Constants ◽  
Different Temperatures ◽  
Kinetics Of

The kinetics of the aquation reaction of the [VO(ida)(bipy)]·2H2O (VO(ida)(bipy)) complex (where ida = iminodiacetate anion and bipy = 2,2’-bipyridine) promoted by [Fe(H2O)6]3+ ions were investigated in aqueous solutions. Spectrophotometric studies were carried out at different temperatures in the range of 293.15–313.15 K. The concentration of the [Fe(H2O)6]3+ (Fe3+) ions was kept within the range of 2 × 10–4 to 8 × 10–4 mol L–1, and the concentration of VO(ida)(bipy) was 1 × 10–3 mol L–1. The values of the observable reaction rate constants were calculated based on the Glint computer program. Furthermore, the mechanism for the aquation of VO(ida)(bipy), induced by Fe(III) ions, has been proposed.

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

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