Multistep Charge Transfers in Stationary Electrode Polarography.

Polcyn, D. S.; Shain, Irving.

doi:10.1021/ac60235a002

Cited by 296 publications

(139 citation statements)

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“…This implies that with the latter enzyme the reduction of the catalytic centre occurs in two-electron steps, the first being slow, the second fast. This occurs only when the second reduction step has a more positive midpoint potential as compared to the first step [14].…”

Section: Discussionmentioning

confidence: 99%

Kinetic Properties of Hxdrogenase Isolated from Desulfovibrio vulgaris (Hildenborough)

Grande

Berkel-Arts

Bregh

et al. 1983

European Journal of Biochemistry

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Hydrogenase of Desulfovibrio vulgaris shows nonlinear kinetics in hydrogen production with both the natural electron carrier, cytochrome c3, and the artificial donor, methyl viologen semiquinone. Increasing concentrations of salt progressively inhibit the hydrogen production, as do increasing amounts of dimethylsulfoxide (MeZSOj. Hydrogen consumption activity does not change up to 30 % (v/v) of MezSO. Preincubation in Me2SO up to 55% (v/v) does not affect the hydrogen uptake or production. The production activity of the enzyme shows an optimum around pH 6. When plotted as a function of redox potential the activity can be fitted to a Nernst equation with n = 1. Midpoint potentials calculated at various values follow approximately the hydrogen electrode to pH 6. Thereafter, there is a shift of about 40 mV to higher redox potentials.Studies in this laboratory on the kinetic properties of the hydrogenase isolated from Megasphaera elsdenii have been reported in a recent series of articles [I -41. It has been found [l] that H2 production activity of M . elsdenii hydrogenase does not follow Michaelis-Menten kinetics with respect to its donors. The kinetics for M . elsdenii enzyme have been explained as being the result of a random mechanism, applicable to both the natural donors, flavodoxin and ferredoxin, as well as to the artificial donor, methyl viologen semiquinone. This deviation from Michaelis-Menten kinetics was first observed for the natural donors. The mathematical model proposed was then tested on the artificial donor methyl viologen. Since the deviation becomes more pronounced at higher methyl viologen semiquinone concentrations, the dimer of the semiquinone had to be taken into account. Therefore the methyl viologen experiments were performed at different salt concentrations since the association constant of the monomer-dimer equilibrium is dependent on salt. It was shown that the enzyme shows different kinetics with the monomer compared to the dimer. Also, salt influences the kinetics, not only by shifting the dimer equilibrium, but also through its effect on the protein itself [2]. A similar salt stimulation has been found by Roessler and Lien [5] for another hydrogenase, isolated from Chlamydomonas reinhardtii. The activity of the M . elsdenii enzyme is furthermore stimulated at low pH, which is a resultant of the effect of pH on the enzyme itself and the higher H + (substrate) concentration [4]. The midpoint potential of the enzyme as derived from initial activity measurement shows the same potential as the hydrogen electrode, at the pH tested, which allows the enzyme to be reduced at relatively low pH. The influence of dimethylsulfoxide (MezSOj and ethylene glycol were also measured to determine whether or not organic solvents influence the enzyme in a way different from salt.Since the hydrogenase isolated from Desulfovihrio vulgaris is a highly active enzyme and also contains 12 iron and Abbreviations. Hepes, 4-(2-hydroxyethyl)-l -piperazineethanesulfonic acid; Mes, 4-morpholineethanesulfonic acid; cy...

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Section: Discussionmentioning

confidence: 99%

Kinetic Properties of Hxdrogenase Isolated from Desulfovibrio vulgaris (Hildenborough)

Grande

Berkel-Arts

Bregh

et al. 1983

European Journal of Biochemistry

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“…Under equilibrium conditions, the stability of intermediate is the best estimated at the medium potential: The dependences of net peak currents and peak potentials on the logarithm of kinetic parameter 1 λ are shown in Figures 2 and 3 log λ = −0.519, which is also marked. For some quasireversible reactions, these critical parameters can be measured by the variation of frequency.…”

Section: Resultsmentioning

confidence: 90%

“…This confirms earlier findings that the response of some two-step electrode reactions may resemble the response of one-electron reaction. 3,8,11 This phenomenon is a consequence of equal kinetic parameters 1 λ and 2 λ , and not of equal standard potentials , E E and the logarithm of frequency, one can determine the logarithm of critical frequency cross log f at which these lines intersect. This frequency is related to the standard rate constant as follows:…”

Section: Resultsmentioning

confidence: 99%

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Theory of Square-wave Voltammetry of Kinetically Controlled Two-step Electrode Reactions

Lovrić¹,

Komorsky‐Lovrić²

2012

Croat. Chem. Acta

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Abstract. An influence of electron transfer kinetics on square-wave voltammograms of two-step electrode reaction is investigated theoretically. A phenomenon of "kinetic burden" of potential inversion is described for the case of equal kinetic parameters. A linear relationship between standard rate constant and the difference between standard potentials of the second and the first charge transfers is demonstrated for the reactions with thermodynamically unstable intermediate. (doi: 10.5562/cca2126)

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“…process is followed by a second reduction reaction involving the product of the· chemical reaction, i.e., the mechanism is of the type E.C.E. (64,65).…”

Section: 2~----------------~--------------~~---------------4-------mentioning

confidence: 99%

Study of the interactions of molten sodium nitrate-potassium nitrate 50 mol % mixture with water vapor and carbon dioxide in air. Final report, June 2, 1980-June 30, 1981

White¹,

Twardoch²

1981

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Multistep Charge Transfers in Stationary Electrode Polarography.

Cited by 296 publications

References 9 publications

Kinetic Properties of Hxdrogenase Isolated from Desulfovibrio vulgaris (Hildenborough)

Kinetic Properties of Hxdrogenase Isolated from Desulfovibrio vulgaris (Hildenborough)

Theory of Square-wave Voltammetry of Kinetically Controlled Two-step Electrode Reactions

Study of the interactions of molten sodium nitrate-potassium nitrate 50 mol % mixture with water vapor and carbon dioxide in air. Final report, June 2, 1980-June 30, 1981

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