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.

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.

The Kinetics of the Formation of the Primary Lactoperoxidase – Hydrogen Peroxide Compound

1971 ◽  
Vol 49 (10) ◽  
pp. 1165-1171 ◽  
Author(s):  
R. James Maguire ◽  
H. Brian Dunford ◽  
Martin Morrison
Keyword(s):  
Hydrogen Peroxide ◽  
Steady State ◽  
Rate Constant ◽  
Order Rate Constant ◽  
Compound I ◽  
Anomalous Effect ◽  
Peroxide Compound ◽  
A Value ◽  
Ph Range ◽  
Kinetics Of

The kinetics of the formation of the primary lactoperoxidase – hydrogen peroxide compound (compound I) at 25 °C have been studied over the pH range 3.0–10.8 by steady state methods. The second-order rate constant k1 is pH-independent over the pH region investigated, having a value of (9.2 ± 0.9) × 106M−1s−1. An anomalous effect of formate buffer on the kinetics of the formation of compound I is reported.

Kinetics of formation of the peroxidatic intermediate from deuteroferriheme and hydrogen peroxide

Biochemistry ◽  
1974 ◽  
Vol 13 (21) ◽  
pp. 4279-4284 ◽  
Author(s):  
Peter Jones ◽  
Kenneth Prudhoe ◽  
Terrence Robson ◽  
Henry C. Kelly
Keyword(s):  
Hydrogen Peroxide ◽  
Kinetics Of Formation ◽  
Kinetics Of

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.

Insight into the degradation of a manganese(III)-citrate complex in aqueous solutions

2011 ◽  
Vol 65 (3) ◽  
Author(s):  
Adrian Topolski
Keyword(s):  
Aqueous Solutions ◽  
Reaction Rate ◽  
Electron Transfer Process ◽  
Ph Profile ◽  
Reduction Potentials ◽  
Citrate Complex ◽  
Basic Solutions ◽  
Ph Range ◽  
Kinetics Of ◽  
Insight Into

AbstractKinetics of the electron transfer process between citrates and manganese(III) ions has been studied in acidic aqueous solutions. Acidification of the reaction mixture increased the reaction rate. The reaction is dependent on pH because there are two main protolytic forms of the Mn(III)-citrate complex in the studied pH range (4.5–6.5). Reduction potentials of Mn(III)/Mn(II) system in acidic and basic solutions as well as protolytic equilibria play a crucial role in understanding the pH profile of the studied system. The rate constants for Mn(III)citH and Mn(III)citH2+ species degradation processes are presented (citH3− and citH22− are trivalent and divalent anions of citric acid, citH4, respectively). Protolytic constant (expressed as pK′a) for Mn(III)citH protonation is estimated and discussed.

The kinetics of fluoride binding by lactoperoxidase

1968 ◽  
Vol 46 (12) ◽  
pp. 1471-1474 ◽  
Author(s):  
Raymond Segal ◽  
H. Brian Dunford ◽  
Martin Morrison
Keyword(s):  
Dissociation Rate ◽  
Specific Rate ◽  
Accurate Analysis ◽  
Binding Reaction ◽  
Reversible Binding ◽  
First Order Kinetics ◽  
Flow Apparatus ◽  
Absorbance Changes ◽  
Ph Range ◽  
Kinetics Of

The kinetics of the reversible binding of fluoride by ferric lactoperoxidase has been studied over the pH range 3.8–5.4 by means of a stopped-flow apparatus. Because of small absorbance changes upon the binding of fluoride by lactoperoxidase, the reaction was driven to completion by addition of a large excess of fluoride. Under these conditions the binding reaction obeys pseudo-first-order kinetics and an accurate analysis of the dissociation rate data is not possible. The results are consistent with a mechanism in which HF binds to the active site which contains no groups capable of ionization in the pH range of the present study. The specific rate constant for the binding reaction of HF to lactoperoxidase is (9.7 ± 0.4) × 102 M−1s−1.

scholarly journals Photodegradation of levofloxacin in aqueous and organic solvents: A kinetic study

2013 ◽  
Vol 63 (2) ◽  
pp. 223-229 ◽  
Author(s):  
Iqbal Ahmad ◽  
Raheela Bano ◽  
Muhammad Ali Sheraz ◽  
Sofia Ahmed ◽  
Tania Mirza ◽  
...  
Keyword(s):  
Dielectric Constant ◽  
Degradation Rate ◽  
Hplc Method ◽  
Ph Profile ◽  
Degree Of Ionization ◽  
First Order ◽  
First Order Kinetics ◽  
Anionic Species ◽  
Ph Range ◽  
Kinetics Of

The kinetics of photodegradation of levofloxacin in solution on UV irradiation in the pH range 2.0-12.0 has been studied using a HPLC method. Levofloxacin undergoes first-order kinetics in the initial stages of the reaction and the apparent first-order rate constants are of the order of 0.167 to 1.807×10-3 min-1. The rate-pH profile is represented by a curve indicating the presence of cationic, dipolar and anionic species during the reaction. The singly ionized form of the molecule is non-fluorescent and is less susceptible to photodegradation. The increase in the degradation rate in the pH range 5.0-9.0 may be due to greater reactivity of the ionized species existing in that range. The rate appears to vary with a change in the degree of ionization of the species present in a particular pH range and their susceptibility to photodegradation. Above pH 9, the decrease in the rate of photodegradation may be a result of deprotonation of the piperazinyl group. The levofloxacin molecule is more stable in the pH range around 7, which is then suitable for formulation purposes. The photodegradation of levofloxacin was found to be affected by the dielectric constant and viscosity of the medium

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