A Kinetic Study of the Reaction of Horseradish Peroxidase with Hydrogen Peroxide

1975 ◽  
Vol 53 (5) ◽  
pp. 495-501 ◽  
Author(s):  
D. Dolman ◽  
G. A. Newell ◽  
M. D. Thurlow ◽  
H. B. Dunford
Keyword(s):  
Hydrogen Peroxide ◽  
Horseradish Peroxidase ◽  
Kinetic Study ◽  
Enzyme Analysis ◽  
Cyanide Binding ◽  
Rate Of Reaction ◽  
Form Compound ◽  
Ph Range ◽  
Kinetics Of ◽  
Ionizable Groups

A kinetic study has been carried out over the pH range of 2.63–9.37 for the reaction of horseradish peroxidase with hydrogen peroxide to form compound 1 of the enzyme. Analysis of the results, indicates that there are two kinetic influencing, ionizable groups on the enzyme with pKa values of 3.2 and 3.9. Protonation of these groups results in a decrease in the rate of reaction of the enzyme with H2O2.A previous study of the kinetics of cyanide binding to horseradish peroxidase (Ellis, W. D. &Dunford, H. B.: Biochemistry 7, 2054–2062 (1968)) has been extended down to pH 2.55, and analysis of these results also indicates the presence of two kinetically important ionizable groups on the enzyme with pKa values of 2.9 and 3.9.

Kinetics of formation of the primary compound (compound I) from hydrogen peroxide and turnip peroxidases

1978 ◽  
Vol 56 (7) ◽  
pp. 702-707 ◽  
Author(s):  
Dominique Job ◽  
Jacques Ricard ◽  
H. Brian Dunford
Keyword(s):  
Hydrogen Peroxide ◽  
Compound I ◽  
Ph Profile ◽  
Glycerol Water ◽  
Binding Reaction ◽  
Cyanide Binding ◽  
Kinetics Of Formation ◽  
Ph Range ◽  
Kinetics Of ◽  
Ionizable Groups

A kinetic study of the reaction of two turnip peroxidases (P1 and P7) with hydrogen peroxide to form the primary oxidized compound (compound I) has been carried out over the pH range from 2,4 to 10.8. In the neutral and acidic pH regions, the rates depend linearly on hydrogen peroxide concentration whereas at alkaline pH values the rates display saturation kinetics. A comparison is made with the cyanide binding reaction to peroxidases since the two reactions are influenced in the same manner by ionization of groups on the native enzymes. Two different ionization processes of peroxidase P1 with pKa values of 3.9 and 10 are required to explain the rate pH profile for the reaction with H2O2. Protonation of the former group and ionization of the latter causes a decrease in the rate of reaction of the enzyme with H2O2. In the case of peroxidase P7 a minimum model involves three ionizable groups with pKa values of 2.5, 4, and 9. Protonation of the former two groups and ionization of the latter lowers the reaction rate. In the pH-independent region, the rate of formation of compound I was measured as a function of temperature. From the Arrhenius plots the activation energy for the reaction was calculated to be 2.9 ± 0.1 kcal/mol for P1 and 5.4 ± 0.3 kcal/mol for P7. However, the rates are independent of viscosity in glycerol–water mixtures up to 30% glycerol.

Studies on Horseradish Peroxidase. VII. A Kinetic Study of the Oxidation of Iodide by Horseradish Peroxidase Compound II

1971 ◽  
Vol 49 (18) ◽  
pp. 3059-3063 ◽  
Author(s):  
R. Roman ◽  
H. B. Dunford ◽  
M. Evett
Keyword(s):  
Ionic Strength ◽  
Horseradish Peroxidase ◽  
Kinetic Study ◽  
Rate Constant ◽  
Ph Dependence ◽  
Order Rate Constant ◽  
Acid Dissociation ◽  
Ph Range ◽  
Compound Ii ◽  
Kinetics Of

The kinetics of the oxidation of iodide ion by horseradish peroxidase compound II have been studied as a function of pH at 25° and ionic strength of 0.11. The logarithm of the second-order rate constant decreases linearly from 2.3 × 105 to 0.1 M−1 s−1 with increasing pH over the pH range 2.7 to 9.0. The pH dependence of the reaction is explained in terms of an acid dissociation outside the pH range of the study.

Studies on Horseradish Peroxidase. XII. A Kinetic Study of the Oxidation of Sulfite and Nitrite by Compounds I and II

1973 ◽  
Vol 51 (4) ◽  
pp. 588-596 ◽  
Author(s):  
R. Roman ◽  
H. B. Dunford
Keyword(s):  
Horseradish Peroxidase ◽  
Ground State ◽  
Ph Dependence ◽  
Intermediate Formation ◽  
Ion Concentration ◽  
Compound I ◽  
Hydrogen Ion Concentration ◽  
Ph Range ◽  
Compound Ii ◽  
Kinetics Of

The kinetics of the oxidation of sulfite and nitrite by horseradish peroxidase compounds I and II have been studied as a function of pH at 25° and ionic strength 0.11. The pH dependence of the rate of the reaction between compound I and sulfite over the pH range 2–7 is interpreted in terms of two ground state enzyme dissociations with pka values of 5.1 and 3.3, and that for the compound II reaction with sulfite in terms of a single ground state enzyme dissociation with a pKa value of 3.9. Whereas the reaction between compound I and sulfite produces the native enzyme without the intermediate formation of compound II, the reaction of compound I with nitrite yields compound II. The second-order rate constants for the reactions of compounds I and II with nitrite increase linearly with increasing hydrogen ion concentration over the pH range 6–8.

scholarly journals Horseradish peroxidase. XXIX. Reactions in water and deuterium oxide: cyanide binding, compound I formation, and reactions of compounds I and II with ferrocyanide

1978 ◽  
Vol 56 (22) ◽  
pp. 2844-2852 ◽  
Author(s):  
H. Brian Dunford ◽  
W. Donald Hewson ◽  
Håkan Steiner
Keyword(s):  
Hydrogen Peroxide ◽  
Horseradish Peroxidase ◽  
Kinetic Isotope Effect ◽  
Deuterium Oxide ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Compound I ◽  
Kinetic Isotope ◽  
Cyanide Binding ◽  
Compound Ii

The kinetics of the reactions of hydrogen peroxide and cyanide with native horseradish peroxidase, as well as reactions of compounds I and II with ferrocyanide have been studied in ordinary water and in deuterium oxide at 25 °C and ionic strength 0.11 using a stopped-flow apparatus. Rate constants for all reactions were measured over a wide range of acidity in both solvents from which equilibrium and kinetic isotope effects were evaluated. Protonation of an ionizable group on the enzyme with a pKa value of 4.15 ± 0.05 in water inhibits the reactions with both hydrogen peroxide and cyanide. A significant kinetic isotope effect, kH/kD = 1.6 ± 0.1, was measured for compound I formation whereas no significant kinetic isotope effect was found for cyanide binding. On the basis of these findings, a partial mechanism for compound I formation is proposed in which the group of pKa 4.15 plays a crucial role. The pH dependencies of the ferrocyanide reaction in the pH interval 4.5–10.8 confirmed the role of an acid group with a pKa of 5.2 for compound I and for compound II a pKa of 8.6 and another with a value lower than that encompassed by the pH range of the study. Equilibrium isotope effects were found but no kinetic isotope effects for either the reaction of compound I or of compound II This suggests that there are no rate-limiting proton transfers in the reactions between ferrocyanide and compounds I and II of horseradish peroxidase. The only reducing substrates which exhibit positive kH/kD values possess a labile proton.

On N-acetylcysteine. Part II. Oxidation of N-acetylcysteine by hydrogen peroxide: kinetic study of the overall process

1994 ◽  
Vol 72 (10) ◽  
pp. 2102-2107 ◽  
Author(s):  
Zohreh Abedinzadeh ◽  
Jlil Arroub ◽  
Monique Gardès-Albert
Keyword(s):  
Hydrogen Peroxide ◽  
Kinetic Study ◽  
Oxidation Kinetics ◽  
Reaction Mechanisms ◽  
Kinetic Data ◽  
Concentration Ratio ◽  
Low Concentration ◽  
Neutral Ph ◽  
Kinetics Of ◽  
Concentration Ratios

The oxidation kinetics of N-acetylcysteine (RSH) by hydrogen peroxide has been studied at neutral pH at different concentration ratios from 0.2 to 20 (4 × 10−4 mol L−1 ≤ [RSH]0 ≤ 2 × 10−2 mol L−1, 10−4 mol L−1 ≤ [H2O2]0 ≤ 10−2 mol L−1). In all the cases studied, N-acetylcystine (RSSR) is the only oxidized product formed. Our kinetic data have focused on the importance of the concentration ratio to reach the stoichiometric oxidation of N-acetylcysteine by hydrogen peroxide. Indeed non-stoichiometric oxidation of RSH occurs at relatively low concentration ratios (R < 2.5) whereas stoichiometric oxidation is observed when R > 2.5. Moreover, it has been shown that in the first minutes of the reaction there is the formation of a complex between RSH and H2O2, the stoichiometry of the complex being RSH concentration-dependent for a given R (R > 2.5). Reaction mechanisms have been quantitatively established and the k values of each step determined.

scholarly journals Photoinitiated Polymerization of 2-Hydroxyethyl Methacrylate by Riboflavin/Triethanolamine in Aqueous Solution: A Kinetic Study

2013 ◽  
Vol 2013 ◽  
pp. 1-7 ◽  
Author(s):  
Iqbal Ahmad ◽  
Kefi Iqbal ◽  
Muhammad Ali Sheraz ◽  
Sofia Ahmed ◽  
Tania Mirza ◽  
...  
Keyword(s):  
Initial Rate ◽  
Hydroxyl Group ◽  
Hydroxyethyl Methacrylate ◽  
First Order ◽  
First Order Kinetics ◽  
Rate Of Polymerization ◽  
Rate Of Reaction ◽  
Ph Range ◽  
Kinetics Of ◽  
Increased Activity

The polymerization of 1–3 M 2-hydroxyethyl methacrylate (HEMA) initiated by riboflavin/triethanolamine system has been studied in the pH range 6.0–9.0. An approximate measure of the kinetics of the reaction during the initial stages (~5% HEMA conversion) has been made to avoid the effect of any variations in the volume of the medium. The concentration of HEMA in polymerized solutions has been determined by a UV spectrophotometric method at 208 nm with a precision of ±3%. The initial rate of polymerization of HEMA follows apparent first-order kinetics and the rates increase with pH. This may be due to the presence of a labile proton on the hydroxyl group of HEMA. The second-order rate constants for the interaction of triethanolamine and HEMA lie in the range of 2.36 to  M−1 s−1 at pH 6.0–9.0 suggesting an increased activity with pH. An increase in the viscosity of HEMA solutions from 1 M to 3 M leads to a decrease in the rate of polymerization probably as a result of the decrease in the reactivity of the flavin triplet state. The effect of pH and viscosity of the medium on the rate of reaction has been evaluated.

The oxidation of hydrogen peroxide by tris(polypyridine) complexes of osmium(III), iron(III), ruthenium(III), and nickel(III) in aqueous media

1986 ◽  
Vol 64 (9) ◽  
pp. 1936-1942 ◽  
Author(s):  
Donal H. Macartney
Keyword(s):  
Hydrogen Peroxide ◽  
Exchange Rate ◽  
Rate Constant ◽  
Aqueous Media ◽  
Activation Parameters ◽  
Exchange Rate Constant ◽  
Oxidation Of Hydrogen ◽  
Polypyridine Complexes ◽  
Ph Range ◽  
Kinetics Of

The stoichiometry and kinetics of the oxidation of hydrogen peroxide by tris(2,2′-bipyridine) and tris(4,4′-dimethyl-2,2′-bipyridine) complexes of osmium(III), iron(III), ruthenium(III), and nickel (III) were studied in acidic and neutral aqueous media at 25 °C and I = 0.50 M (LiCF3SO3). The reaction 2M(bpy)33+ + H2O2 → 2M(bpy)32+ + O2 + 2H+ is observed with quantitative yields of dioxygen gas. The observed rate constants displayed an inverse acid dependence over the pH range 6.0–8.5; kobsd = k1 + k2K1/[H+], attributed to the oxidations of H2O2(k1) and HO2− (k2). An application of the Marcus theory relationship to the cross-reaction data gave a self-exchange rate constant of 10−2–10−1 M−1 s−1 for the HO2−/HO2 couple. The electron exchange rate constant is evaluated in terms of the inner-sphere and solvent reorganizational barriers and is compared to values reported for other small molecule couples. Rate and activation parameters for the reduction of the nickel(III) complexes by the hydroxide ion have been determined and are compared with the corresponding values for other metal tris(poly pyridine) complexes.

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