Kinetic studies of the reduction of neutrophil cytochrome b-558 by dithionite

The reduction with dithionite of neutrophil cytochrome b-558, implicated in superoxide generation by activated neutrophils, was investigated by a stopped-flow technique in non-ionic-detergent extracts of the membranes and in crude membrane particles. The dependence of the pseudo-first-order rate constants on the concentration of dithionite was consistent with a mechanism of reduction that involves the dithionite anion monomer SO2.- as the reactive species. The estimated second-order rate constant was 7.8 × 10(6) M-1 × S-1 for Lubrol PX-solubilized cytochrome b-558 and 5.1 × 10(6) M-1 × S-1 for the membrane-bound protein. The similarity of the kinetic constants suggests that solubilization did not introduce gross changes in the reactive site. Imidazole and p-chloromercuribenzoate, known as inhibitors of NADPH oxidase, did not affect significantly cytochrome b-558 reduction rates. The reaction rate of cytochrome b-558 with dithionite exhibited a near-zero activation energy. The first-order rate constant for reduction decreased with increasing ionic strength, indicating a positive effective charge on the reacting protein.

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The polymerization of ethylene on chromium oxide catalysts I. Kinetic studies

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1972.0117 ◽

1972 ◽

Vol 329 (1579) ◽

pp. 361-373 ◽

Cited By ~ 13

Keyword(s):

Rate Constant ◽

Initial Pressure ◽

Kinetic Studies ◽

Order Rate Constant ◽

Polymerization Reaction ◽

First Order ◽

Ethylene Pressure ◽

Order Rate ◽

Chromium Vi ◽

Chromium Oxide Catalysts

The rates of polymerization of ethylene on a supported chromium (VI) oxide Phillips catalysts have been measured. Catalysts were calcined in air at 460 °C and activated by pretreatment with ethylene at 300 °C. With increasing pretreatment times the activity of the catalyst increased to a maximum, after which over-reduction occurred and the activity fell. The products of the pretreatment process were water, carbon dioxide and a trace of butenes. Rates of polymerization were first order in ethylene pressure over the temperature range studied ( – 95 to 150 °C). The first order rate constant was sensitive to the initial pressure of ethylene added to the catalyst at the temperature at which the polymerization reaction was carried out. The results are explicable in terms of the production of active centres in the catalyst surface during contact with ethylene at 300 °C. Subsequent evacuation at 300 °C produced from some of these centres sites which had to be reactivated by adsorption of ethylene at low temperatures. The extent of re-activation increased with increasing ethylene pressure. The variation of first order rate constant with temperature showed a maximum at ca . – 23 °C and an apparent activation energy of 0.8 kJ mol -1 for the range –95 to – 23 °C. At temperatures above 227 °C the rate of polymerization was extremely slow.

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The Dephosphorylation of Adenosine 5′ -Triphosphate in a Binary and Ternary Zn2+ Complex

Zeitschrift für Naturforschung C ◽

10.1515/znc-1974-11-1205 ◽

1974 ◽

Vol 29 (11-12) ◽

pp. 680-682 ◽

Cited By ~ 5

Author(s):

Peter Amsler ◽

David Buisson ◽

Helmut Sigel

Keyword(s):

Rate Constant ◽

Ternary Complex ◽

Order Rate Constant ◽

Reactive Species ◽

Ph Optimum ◽

First Order ◽

Order Rate

The dephosphorylation of ATP was characterized by determining the dependence of the first-order rate constant on pH in the absence and presence of Zn2+ and together with Zn2+ and 2,2′-bipyridyl. The Zn2+-accelerated reaction passes through a pH optimum at about 8. The decrease in the rate at higher pH is due to the formation of Zn(ATP) (OH)3-; this species is relatively insensitive towards dephosphorylation. It is concluded that Zn(ATP)2- is the reactive species and that the interaction between N (7) and Zn2+ in this complex is crucial for its reactivity. In the presence of 2,2′-bipyridyl (Bipy) the ternary complex, Zn (Bipy) (ATP)2-, is formed which is rather stable towards dephosphorylation. It is suggested that the described effects of acceleration and inhibition are helpful for understanding the recycled processes in nature.

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Kinetics of reconstitution of apotyrosinase by copper

Biochemistry and Cell Biology ◽

10.1139/o90-067 ◽

1990 ◽

Vol 68 (2) ◽

pp. 476-479

Author(s):

Donald C. Wigfield ◽

Douglas M. Goltz

Keyword(s):

Rate Constant ◽

Copper Concentration ◽

Copper Ions ◽

Copper Ion ◽

Order Rate Constant ◽

First Order ◽

Order Rate ◽

Pseudo First Order ◽

Rate Limiting ◽

Kinetics Of

The kinetics of the reconstitution reaction of apotyrosinase with copper (II) ions are reported. The reaction is pseudo first order with respect to apoenzyme and the values of these pseudo first order rate constants are reported as a function of copper (II) concentration. Two copper ions bind to apoenzyme, and if the second one is rate limiting, the kinetically relevant copper concentration is the copper originally added minus the amount used in binding the first copper ion to enzyme. This modified copper concentration is linearly related to the magnitude of the pseudo first order rate constant, up to a copper concentration of 1.25 × 10−4 M (10-fold excess), giving a second order rate constant of 7.67 × 102 ± 0.93 × 102 M−1∙s−1.Key words: apotyrosinase, copper, tyrosinase.

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Inactivation of the endogenous argininosuccinate lyase activity of duck δ-crystallin by modification of an essential histidine residue with diethyl pyrocarbonate

Biochemical Journal ◽

10.1042/bj2930537 ◽

1993 ◽

Vol 293 (2) ◽

pp. 537-544 ◽

Cited By ~ 8

Author(s):

H J Lee ◽

S H Chiou ◽

G G Chang

Keyword(s):

Enzyme Activity ◽

Rate Constant ◽

Order Rate Constant ◽

Histidine Residue ◽

Argininosuccinate Lyase ◽

First Order ◽

Diethyl Pyrocarbonate ◽

Order Rate ◽

Lyase Activity ◽

Pseudo First Order

The argininosuccinate lyase activity of duck delta-crystallin was inactivated by diethyl pyrocarbonate at 0 degrees C and pH 7.5. The inactivation followed pseudo-first-order kinetics after appropriate correction for the decomposition of the reagent during the modification period. The plot of the observed pseudo-first-order rate constant versus diethyl pyrocarbonate concentration in the range of 0.17-1.7 mM was linear and went through the origin with a second-order rate constant of 1.45 +/- 0.1 M-1.s-1. The double-logarithmic plot was also linear, with slope of 1.13, which suggested a 1:1 stoichiometry for the reaction between diethyl pyrocarbonate and delta-crystallin. L-Arginine, L-norvaline or L-citrulline protected the argininosuccinate lyase activity of delta-crystallin from diethyl pyrocarbonate inactivation. The dissociation constants for the delta-crystallin-L-arginine and delta-crystallin-L-citrulline binary complexes, determined by the protection experiments, were 4.2 +/- 0.2 and 0.12 +/- 0.04 mM respectively. Fumarate alone had no protective effect. However, fumarate plus L-arginine gave synergistic protection with a ligand binding interacting factor of 0.12 +/- 0.02. The double-protection data conformed to a random Uni Bi kinetic mechanism. Fluorescence-quenching studies indicated that the modified delta-crystallin had minimum, if any, conformational changes as compared with the native delta-crystallin. Inactivation of the enzyme activity was accompanied by an increasing absorbance at 240 nm of the protein. The absorption near 280 nm did not change. Treatment of the modified protein with hydroxylamine regenerated the enzyme activity to the original level. These results strongly indicated the modification of an essential histidine residue. Calculation from the 240 nm absorption changes indicated that only one histidine residue per subunit was modified by the reagent. This super-active histidine residue has a pKa value of approximately 6.8 and acts as a general acid-base catalyst in the enzyme reaction mechanism. Our experimental data are compatible with an E1cB mechanism [Raushel (1984) Arch. Biochem. Biophys. 232, 520-525] for the argininosuccinate lyase with the essential histidine residue close to the arginine-binding domain of delta-crystallin. L-Citrulline, after binding to this domain, might form an extra hydrogen bond with the essential histidine residue.

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The Initial Stages of the Pyrolysis of Dimethyl Ether

Canadian Journal of Chemistry ◽

10.1139/v75-388 ◽

1975 ◽

Vol 53 (18) ◽

pp. 2742-2747 ◽

Cited By ~ 29

Author(s):

Philip D. Pacey

Keyword(s):

Dimethyl Ether ◽

Rate Constant ◽

Arrhenius Plot ◽

Flow System ◽

Order Rate Constant ◽

Chain Termination ◽

Rate Coefficients ◽

First Order ◽

Order Rate ◽

Initiation Reaction

Dimethyl ether was pyrolized in a flow system at 782–936 K and 25–395 Torr with conversions from 0.2–10%. Product analyses were consistent with a simple Rice–Herzfeld mechanism with most chain termination by the recombination of CH3 radicals. The rate coefficients for both the initiation and termination reactions appeared to be slightly pressure dependent. The first-order rate constant for the initiation reaction,[Formula: see text]calculated from the rate of C2H6 formation, was k1 = 1015.0±0.5exp (−318 ± 8 kJ mol−1/RT) s−1, corresponding to ΔHf0(CH3O) = −5 ± 8 kJmol−1. Comparison of CH4 and C2H6 yields enabled calculation of the rate constant for the reaction of CH3 with dimethyl ether. From 373−936 K, the Arrhenius plot for this reaction is a curve.

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Visual Interpretation of the Meaning of kcat/KM in Enzyme Kinetics

10.1101/2021.12.09.471995 ◽

2021 ◽

Author(s):

Chiwook Park

Keyword(s):

Transition State ◽

Enzyme Kinetics ◽

Rate Constant ◽

Reaction Rate ◽

Reaction Pathway ◽

Order Rate Constant ◽

Reaction Energy ◽

Energy Diagram ◽

Order Rate ◽

Main Challenge

kcat and kcat/KM are the two fundamental kinetic parameters in enzyme kinetics. kcat is the first-order rate constant that determines the reaction rate when the enzyme is fully occupied at a saturating concentration of the substrate. kcat/KM is the second-order rate constant that determines the reaction rate when the enzyme is mostly free at a very low concentration of the substrate. Both parameters provide critical information on how the enzyme lowers the energy barriers along the reaction pathway for catalysis. However, it is surprising how often kcat/KM is used inappropriately as a composite parameter derived by dividing kcat with KM to assess both catalytic power and affinity to the substrate of the enzyme. The main challenge in explaining the true meaning of kcat/KM is the difficulty to demonstrate how the reaction energetics of enzyme catalysis determines kcat/KM in a simple way. Here, I report a step-by-step demonstration on how to visualize the meaning of kcat/KM on the reaction energy diagram. By using the reciprocal form of the expression of kcat/KM with the elementary rate constants in kinetic models, I show that kcat/KM is a harmonic sum of several kinetic terms that correspond to the heights of the transition states relative to the free enzyme. Then, I demonstrate that the height of the highest transition state has the dominant influence on kcat/KM, i. e. the step with the highest transition state is the limiting step for kcat/KM. The visualization of the meaning of kcat/KM on the reaction energy diagram offers an intuitive way to understand all the known properties of kcat/KM, including the Haldane relationship.

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On the Interaction Between Human Plasma Kallikrein and C1-Esterase Inhibitor

Thrombosis and Haemostasis ◽

10.1055/s-0038-1657360 ◽

1983 ◽

Vol 49 (03) ◽

pp. 193-195 ◽

Cited By ~ 11

Author(s):

Torbjörn Nilsson

Keyword(s):

Dissociation Constant ◽

Human Plasma ◽

Rate Constant ◽

Enzyme Inhibitor ◽

Order Rate Constant ◽

Second Order ◽

Plasma Kallikrein ◽

First Order ◽

Order Rate ◽

Esterase Inhibitor

SummaryThe kinetics of the reaction between human plasma kallikrein and CĪ-esterase inhibitor was studied in a purified system. By monitoring the inhibition reaction for extended periods of time, it was found to proceed in two consecutive steps, a fast reversible second-order binding step followed by a slower, irreversible first-order transition. The rate constants in this reaction model were determined, as well as the dissociation constant of the initial, reversible enzyme-inhibitor complex. Thus, at 37° C the second-order rate constant was found to be 5 · 104 M -1 · s-1, the first order rate constant was 5 · 10-4 s-1 and the dissociation constant K was 1.5 · 10-8 M. Heparin (28 U/ml) and 6-aminohexanoic acid (10 mM) had no effect on the k1 of the of the reaction.

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Kinetics of Reactions of 8-Quinolinol and Acetate with Hydroxyaluminum Species in Aqueous Solutions. 1. Polynuclear Hydroxyaluminum Cations

Canadian Journal of Chemistry ◽

10.1139/v71-274 ◽

1971 ◽

Vol 49 (10) ◽

pp. 1683-1687 ◽

Cited By ~ 14

Author(s):

R. C. Turner ◽

Wan Sulaiman

Keyword(s):

Acetic Acid ◽

Rate Constant ◽

Empirical Equation ◽

Decomposition Reaction ◽

Order Rate Constant ◽

Acetate Concentration ◽

First Order ◽

Order Rate ◽

Pseudo First Order ◽

Kinetics Of

The effect of varying 8-quinolinol and acetate concentration on the rate of decomposition of poly-nuclear hydroxyaluminum cations was studied. It was found that the concentration of the undissociated 8-quinolinol and acetic acid molecules determined the magnitude of the first order rate constant for the decomposition of the polynuclear hydroxyaluminum cations, except when the acetate concentrations were relatively high. With high acetate concentrations, it appeared that polynuclear acetate species were involved in the reactions. An empirical equation was developed showing the effect of 8-quinolinol and acetic acid molecule concentrations on the pseudo first order rate constant for the decomposition reaction.

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