Resolution of Stopped-Flow Kinetic Data for Second-Order Reactions with Rate Constants up to 108M-1s-1Involving Large Concentration Gradients. Experimental Comparison Using Three Independent Approaches

1996 ◽  
Vol 100 (42) ◽  
pp. 16925-16933 ◽  
Author(s):  
Brian C. Dunn ◽  
Nancy E. Meagher ◽  
David B. Rorabacher
Keyword(s):  
Rate Constants ◽  
Kinetic Data ◽  
Second Order ◽  
Large Concentration ◽  
Experimental Comparison ◽  
Stopped Flow ◽  
Concentration Gradients

scholarly journals A method for extracting rate constants from initial rates of stopped-flow kinetic data: application to a physiological electron-transfer reaction

1993 ◽  
Vol 294 (1) ◽  
pp. 211-213 ◽  
Author(s):  
H B Brooks ◽  
V L Davidson
Keyword(s):  
Electron Transfer ◽  
Rate Constants ◽  
Kinetic Data ◽  
Transfer Reaction ◽  
Dissociation Constants ◽  
Accurate Method ◽  
Electron Transfer Reaction ◽  
Stopped Flow ◽  
Methylamine Dehydrogenase ◽  
Substrate Complex

The most commonly used methods for analysis of stopped-flow kinetic data require performing a series of measurements in which one reactant is varied at concentrations significantly greater than the concentration of the other reactant. For enzyme-catalysed reactions this may not be possible, because the dissociation constants for the enzyme-substrate complex are often of the same order of magnitude as the high concentrations of enzyme that must frequently be used in stopped-flow studies. An alternative method of data analysis is presented which allows the determination of microscopic rate constants from initial rates of stopped-flow kinetic data in which substrate is varied in a range of concentrations approximately the same as the enzyme. This method also provides a simple and accurate method for determining k4, the rate of the reverse reaction. This method has been used to describe a physiological electron transfer reaction between a quinoprotein, methylamine dehydrogenase, and a copper protein, amicyanin. At 20 degrees C, the rate of the electron-transfer reaction from methylamine dehydrogenase to amicyanin was 24 s-1, and the dissociation constant for complex-formation was 1.9 microM.

scholarly journals Kinetics of Reduction of Fe(III) Complexes by Outer Membrane Cytochromes MtrC and OmcA of Shewanella oneidensis MR-1

2008 ◽  
Vol 74 (21) ◽  
pp. 6746-6755 ◽  
Author(s):  
Zheming Wang ◽  
Chongxuan Liu ◽  
Xuelin Wang ◽  
Matthew J. Marshall ◽  
John M. Zachara ◽  
...  
Keyword(s):  
Redox Potential ◽  
Outer Membrane ◽  
Kinetic Data ◽  
Shewanella Oneidensis ◽  
Reorganization Energy ◽  
Second Order ◽  
Metal Species ◽  
Stopped Flow ◽  
Kinetics Of ◽  
Kinetics Of Reduction

ABSTRACT Because of their cell surface locations, the outer membrane c-type cytochromes MtrC and OmcA of Shewanella oneidensis MR-1 have been suggested to be the terminal reductases for a range of redox-reactive metals that form poorly soluble solids or that do not readily cross the outer membrane. In this work, we determined the kinetics of reduction of a series of Fe(III) complexes with citrate, nitrilotriacetic acid (NTA), and EDTA by MtrC and OmcA using a stopped-flow technique in combination with theoretical computation methods. Stopped-flow kinetic data showed that the reaction proceeded in two stages, a fast stage that was completed in less than 1 s, followed by a second, relatively slower stage. For a given complex, electron transfer by MtrC was faster than that by OmcA. For a given cytochrome, the reaction was completed in the order Fe-EDTA > Fe-NTA > Fe-citrate. The kinetic data could be modeled by two parallel second-order bimolecular redox reactions with second-order rate constants ranging from 0.872 μM−1 s−1 for the reaction between MtrC and the Fe-EDTA complex to 0.012 μM−1 s−1 for the reaction between OmcA and Fe-citrate. The biphasic reaction kinetics was attributed to redox potential differences among the heme groups or redox site heterogeneity within the cytochromes. The results of redox potential and reorganization energy calculations showed that the reaction rate was influenced mostly by the relatively large reorganization energy. The results demonstrate that ligand complexation plays an important role in microbial dissimilatory reduction and mineral transformation of iron, as well as other redox-sensitive metal species in nature.

Kinetic and thermodynamic control of pseudobase formation from C-3 substituted 1-methylquinolinium cations

1984 ◽  
Vol 62 (7) ◽  
pp. 1301-1307 ◽  
Author(s):  
John W. Bunting ◽  
Norman P. Fitzgerald
Keyword(s):  
Aqueous Solutions ◽  
Rate Constants ◽  
Kinetic Data ◽  
Mixing Time ◽  
Equilibrium Constants ◽  
Substituent Effects ◽  
Stopped Flow ◽  
Thermodynamic Control ◽  
Preferred Species ◽  
Substituted 1

The kinetic and thermodynamic control of pseudobase formation from 3-W-1-methylquinolinium cations has been studied for a variety of substituents (W). Spectral data indicate that, in both aqueous and methanolic solution, the C-2 pseudobases predominate at equilibrium for W = H and Br, while the C-4 pseudobases are the thermodynamically preferred species for W = CONH2, CO2CH3, CN, and NO2. Stopped-flow studies indicate that in all cases the C-2 pseudobases are the kineticallycontrolled products upon basification of the aqueous solutions of these cations. Equilibrium constants (pKR+) have been measured for pseudobase formation at both C-2 and C-4 for each W in all cases where they are experimentally accessible. Substituent effects upon [Formula: see text] correlate with σm for W, while [Formula: see text] depends upon σp−. These substituent effects allow the prediction of [Formula: see text] and [Formula: see text] for the 1-methylquinolinium cation. Rates of C-2 to C-4 pseudobase equilibration have been measured in all cases where the latter species is thermodynamically more stable. These kinetic data allow the evaluation of rate constants for C-4 pseudobase equilibration with each cation. In all cases except W = CN, C-2 pseudobase formation is complete within the mixing time of the stopped-flow instrument.

Kinetic and Mechanistic Study on the Reactions of [Pd(dien)H2O]2+ and [Pt(dien)H2O]2+ with L-Cysteine and S-Methyl-L-cysteine

2005 ◽  
Vol 58 (7) ◽  
pp. 544 ◽  
Author(s):  
Biljana V. Petrović ◽  
Živadin D. Bugarčić
Keyword(s):  
Rate Constants ◽  
Activation Parameters ◽  
Second Order ◽  
Mechanistic Study ◽  
Stopped Flow ◽  
Substitution Reactions ◽  
Order Rate ◽  
Increase With Increase ◽  
Naclo4 Solution ◽  
Entropy Of Activation

The reactions of [Pd(dien)H2O]2+ and [Pt(dien)H2O]2+ (dien = diethylenetriamine or 1,5-diamino-3-azapentane) with l-cysteine and S-methyl-l-cysteine were studied in an aqueous 0.10 M NaClO4 solution using stopped-flow and conventional UV-vis spectrophotometry. The second-order rate constants for the reactions of [Pd(dien)H2O]2+ at pH 1.0 are k1298 = (9.11 ± 0.11) × 102 M−1 s−1 for l-cysteine, and k1298 = (33.79 ± 0.63) × 102 M−1 s−1 for S-methyl-l-cysteine. The second-order rate constants for the reactions of [Pt(dien)H2O]2+ at pH 1.0 with l-cysteine is k1298 = (1.28 ± 0.08) × 10−2 M−1 s−1 and for S-methyl-l-cysteine is k1298 = (3.87 ± 0.02) × 10−2 M−1 s−1. Activation parameters were determined for all reactions, and the negative values of entropy of activation support an associative complex formation mechanism. Substitution reactions were also studied at pH 0.5, 1.0, and 1.5. The rate constants increase with increase in pH. These results are discussed in terms of protolitic equilibrium.

scholarly journals Reactions of cytochrome c oxidase with sodium dithionite

1983 ◽  
Vol 209 (1) ◽  
pp. 175-182 ◽  
Author(s):  
G D Jones ◽  
M G Jones ◽  
M T Wilson ◽  
M Brunori ◽  
A Colosimo ◽  
...  
Keyword(s):  
Cytochrome C ◽  
Cytochrome C Oxidase ◽  
Charge Distribution ◽  
Rate Constants ◽  
Sodium Dithionite ◽  
Second Order ◽  
Stopped Flow ◽  
Entry Site ◽  
Redox Proteins ◽  
Order Rate

The reduction of cytochrome c oxidase (EC 1.9.3.1) by dithionite was investigated by stopped-flow spectrophotometry and flow-flash techniques in the presence of CO. Of the two haem groups present in the enzyme, that associated with cytochrome alpha is the first reduced. The second-order rate constants for reduction of a number of redox proteins (cytochrome c, stellacyanin and azurin) by the S2O4(2-) and SO2.- anions are reported, and the values are compared with those determined for cytochrome c oxidase. These results are discussed in terms of the accessibility and charge distribution of the electron-entry site of cytochrome c oxidase.

scholarly journals About the kinetics and mechanism of the reactions of 4-(2-pyridylazo)-resorcinol, with Zn2+, Cu2+ and Zn2++Cu2+ equimolar mixtures, in aqueous solutions

2003 ◽  
Vol 28 (1) ◽  
pp. 55-62 ◽  
Author(s):  
A. V. Rossi ◽  
M. Tubino
Keyword(s):  
Aqueous Solution ◽  
Aqueous Solutions ◽  
Rate Constants ◽  
Kinetic Data ◽  
Kinetics And Mechanism ◽  
Borate Buffer ◽  
Water Molecules ◽  
Stopped Flow ◽  
Solution Ph ◽  
Unique Species

The kinetics and mechanism of the reactions between 4(2pyridylazo)-resorcinol and Zn2+, Cu2+ and Zn2++Cu2+ equimolar mixtures were studied. The reactions were performed in aqueous solution (pH = 8.5, borate buffer) and monitored spectrophotometrically at 500 nm using stopped-flow technique. Spectral and kinetic data indicate that the Zn2++Cu2+ equimolar mixture behaves as an unique species and it can be attributed to the interactions of Zn2+ and of Cu2+ with water molecules in the aqueous solution. A mechanism is proposed and the rate constants are calculated.

scholarly journals The reduction of Pseudomonas cytochrome c551 oxidase by chromous ions

1977 ◽  
Vol 163 (3) ◽  
pp. 629-632 ◽  
Author(s):  
D Barber ◽  
S R Parr ◽  
C Greenwood
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Rate Constants ◽  
Second Order ◽  
Stopped Flow ◽  
Difference Spectra ◽  
Order Rate ◽  
Flow Apparatus ◽  
Cytochrome C551

The reduction of cytochrome c551 oxidase from Pseudomonas aeruginosa by Cr2+ ions was followed in the stopped-flow apparatus at a number of wavelengths. The c-haem reduction proceeded in a biphasic fashion with second-order rate constants of 2.6 X 10(5)M-1-S-1 and 4.8 X 10(4)M-1-S-1 at 25 degrees C, whereas the biphasic reduction of the d1-haem appeared to be independent of reductant concentration with rate constants of approx. 1.0S-1 and 0.25S-1 respectively. The kinetically determined difference spectra (reduced minus oxidized) for the c- and d1-haems are presented.

Inhibition in Purified Systems and in Human Plasma of Chimaeric Plasminogen Activators Consisting of the NH2-Terminal Region of Tissue-Type Plasminogen Activator and the COOH-Terminal Region of UrokinaseType Plasminogen Activator

1988 ◽  
Vol 60 (02) ◽  
pp. 247-250 ◽  
Author(s):  
H R Lijnen ◽  
L Nelles ◽  
B Van Hoef ◽  
F De Cock ◽  
D Collen
Keyword(s):  
Plasminogen Activator ◽  
Rate Constants ◽  
Plasminogen Activators ◽  
Second Order ◽  
Tissue Type ◽  
Single Chain ◽  
Chain Molecules ◽  
Order Rate ◽  
Type Plasminogen Activator ◽  
Urokinase Type Plasminogen Activator

SummaryRecombinant chimaeric molecules between tissue-type plasminogen activator (t-PA) and single chain urokinase-type plasminogen activator (scu-PA) or two chain urokinase-type plasminogen activator (tcu-PA) have intact enzymatic properties of scu-PA or tcu-PA towards natural and synthetic substrates (Nelles et al., J Biol Chem 1987; 262: 10855-10862). In the present study, we have compared the reactivity with inhibitors of both the single chain and two chain variants of recombinant u-PA and two recombinant chimaeric molecules between t-PA and scu-PA (t-PA/u-PA-s: amino acids 1-263 of t-PA and 144-411 of u-PA; t-PA/u-PA-e: amino acids 1-274 of t-PA and 138-411 of u-PA). Incubation with human plasma in the absence of a fibrin clot for 3 h at 37° C at equipotent concentrations (50% clot lysis in 2 h), resulted in significant fibrinogen breakdown (to about 40% of the normal value) for all two chain molecules, but not for their single chain counterparts. Preincubation of the plasminogen activators with plasma for 3 h at 37° C, resulted in complete inhibition of the fibrinolytic potency of the two chain molecules but did not alter the potency of the single chain molecules. Inhibition of the two chain molecules occurred with a t½ of approximately 45 min. The two chain variants were inhibited by the synthetic urokinase inhibitor Glu-Gly-Arg-CH2CCl with apparent second-order rate constants of 8,000-10,000 M−1s−1, by purified α2-antiplasmin with second-order rate constants of about 300 M−1s−1, and by plasminogen activator inhibitor-1 (PAI-1) with second-order rate constants of approximately 2 × 107 M−1s−1.It is concluded that the reactivity of single chain and two chain forms of t-PA/u-PA chimaers with inhibitors is very similar to that of the single and two chain forms of intact u-PA.

Determination of rate constants of redox reactions of second order from current-less potential-time curves by a simplified graphical-numerical method

1983 ◽  
Vol 48 (5) ◽  
pp. 1358-1367 ◽  
Author(s):  
Antonín Tockstein ◽  
František Skopal
Keyword(s):  
Numerical Method ◽  
Explicit Form ◽  
Rate Constant ◽  
Optimization Algorithm ◽  
Rate Constants ◽  
Redox Reactions ◽  
Second Order ◽  
Wide Region ◽  
Recurrent Formula

A method for constructing curves is proposed that are linear in a wide region and from whose slopes it is possible to determine the rate constant, if a parameter, θ, is calculated numerically from a rapidly converging recurrent formula or from its explicit form. The values of rate constants and parameter θ thus simply found are compared with those found by an optimization algorithm on a computer; the deviations do not exceed ±10%.

Oxidation scheme of symmetrically disulphonated naphthidines with cerium(IV) sulphate

1981 ◽  
Vol 46 (3) ◽  
pp. 561-572 ◽  
Author(s):  
Karel Komers
Keyword(s):  
Sulphuric Acid ◽  
Rate Constants ◽  
Oxidation Product ◽  
Side Reaction ◽  
Reaction Scheme ◽  
Second Order ◽  
Intermediate Products ◽  
Stable Intermediate ◽  
Starting Compound ◽  
Oxidation Agent

The author derived theoretical dependences of preasymptotic slopes of the currentless E-t curves (potential of an indicator redox electrode against time) on the number of equivalents, n, of added oxidation agent, assuming a reaction scheme of two consecutive concurrent second-order reactions involving the formation of intermediate products ( a side reaction of the starting compound with the final oxidation product leading to an adduct, which undergoes consecutive bimolecular oxidations leading again to the final product). The dependences enable to determine the type of the relatively stable intermediate products and the ratios of the rate constants. The theory was applied to the oxidation of four symmetrically disulphonated naphthidines with cerium(IV) sulphate in aqueous sulphuric acid and the results were substantiated spectrophotometrically

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