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.

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. XI. On the Nature of Compounds I and II as Determined from the Kinetics of the Oxidation of Ferrocyanide

1973 ◽  
Vol 51 (4) ◽  
pp. 582-587 ◽  
Author(s):  
M. L. Cotton ◽  
H. B. Dunford
Keyword(s):  
Horseradish Peroxidase ◽  
Rate Constant ◽  
Active Sites ◽  
Ph Dependence ◽  
Order Rate Constant ◽  
Second Order ◽  
Compound I ◽  
Order Rate ◽  
Compound Ii ◽  
Kinetics Of

In order to investigate the nature of compounds I and II of horseradish peroxidase, the kinetics were studied of ferrocyanide oxidation catalyzed by these compounds which were prepared from three different oxidizing agents. The pH dependence of the apparent second-order rate constant for ferrocyanide oxidation by compound I, prepared from ethyl hydroperoxide and m-chloroperbenzoic acid, was interpreted in terms of an ionization on the enzyme with a pKa = 5.3, identical to that reported previously for hydrogen peroxide. The second-order rate constant for the compound II-ferrocyanide reaction also showed the same pH dependence for the three oxidizing substrates. However, with more accurate results, the compound II-ferrocyanide reaction was reinterpreted in terms of a single ionization with pKa = 8.5. The same dependence of ferrocyanide oxidation on pH suggests structurally identical active sites for compounds I and II prepared from the three different oxidizing substrates.

Kinetics of the oxidation of reduced nicotinamide adenine dinucleotide by horseradish peroxidase compounds I and II

1986 ◽  
Vol 64 (4) ◽  
pp. 323-327 ◽  
Author(s):  
Mohammed A. Kashem ◽  
H. Brian Dunford
Keyword(s):  
Horseradish Peroxidase ◽  
Active Site ◽  
Nicotinamide Adenine Dinucleotide ◽  
Ph Dependence ◽  
Transient State ◽  
Nicotinamide Adenine ◽  
Compound I ◽  
Single Ionization ◽  
Reduced Nicotinamide Adenine Dinucleotide ◽  
Kinetics Of

The transient state kinetics of the oxidation of reduced nicotinamide adenine dinucleotide (NADH) by horseradish peroxidase compound I and II (HRP-I and HRP-II) was investigated as a function of pH at 25.0 °C in aqueous solutions of ionic strength 0.11 using both a stopped-flow apparatus and a conventional spectrophotometer. In agreement with studies using many other substrates, the pH dependence of the HRP-I–NADH reaction can be explained in terms of a single ionization of pKa = 4.7 ± 0.5 at the active site of HRP-I. Contrary to studies with other substrates, the pH dependence of the HRP-H–NADH reaction can be interpreted in terms of a single ionization with pKa of 4.2 ± 1.4 at the active site of HRP-II. An apparent reversibility of the HRP-II–NADH reaction was observed. Over the pH range of 4–10 the rate constant for the reaction of HRP-I with NADH varied from 2.6 × 105 to5.6 × 102 M−1 s−1 and of HRP-II with NADH varied from 4.4 × 104 to 4.1 M−1 s−1. These rate constants must be taken into consideration to explain quantitatively the oxidase reaction of horseradish peroxidase with NADH.

Horseradish peroxidase. XLII. Oxidations of L-tyrosine and 3,5-diiodo-L-tyrosine by compound II

1980 ◽  
Vol 58 (11) ◽  
pp. 1270-1276 ◽  
Author(s):  
Isobel M. Ralston ◽  
H. Brian Dunford
Keyword(s):  
Horseradish Peroxidase ◽  
Reaction Rate ◽  
Acid Group ◽  
Amino Groups ◽  
Compound I ◽  
Ph Profile ◽  
Rate Versus ◽  
Phenolic Group ◽  
Ph Range ◽  
Compound Ii

The oxidations of both L-tyrosine and 3,5-diiodo-L-tyrosine by compound II of horseradish peroxidase were studied over the pH range of approximately 3 to 10 at 25 °C and at a constant ionic strength of 0.11. The rate versus pH profile for the tyrosine – compound II reaction illustrates the influences of at least two acid group ionizations. An enzyme dissociation (pKa ~ 6.2) has a small effect on the reaction rate; whereas, a second pKa of 9.2, which may be attributed to either the enzyme or substrate, has a greater influence on the rate. The oxidation of tyrosine by compound II is fastest at pH 7.6. In the case of the diiodotyrosine – compound II reaction, three acid dissociations are necessary to describe the plot of log (kapp) versus pH. These include two enzyme pKa values of 3.6 and 8.6, and one substrate pKa of 6.6. The rate optimum for the reaction occurs at pH 5.2 and deprotonation of the phenolic group of diiodotyrosine results in a dramatic decrease in kapp. Diiodotyrosine is required in only a 0.5 M equivalent for the conversion of horseradish peroxidase compound I to compound II. The diiodotyrosine pKa values were estimated as 6.4 and 9.4 for the phenolic and amino groups, respectively.

Kinetics of the oxidation of Pu(IV) by manganese dioxide

2002 ◽  
Vol 90 (2) ◽  
Author(s):  
A. Morgenstern ◽  
Gregory R. Choppin
Keyword(s):  
Manganese Dioxide ◽  
Rate Equation ◽  
Oxidation Reaction ◽  
Hydrogen Ion ◽  
Ion Concentration ◽  
Hydrogen Ion Concentration ◽  
First Order ◽  
Order Dependence ◽  
Ph Range ◽  
Kinetics Of

SummaryThe kinetics of the oxidation of plutonium(IV) by manganese dioxide were studied in 1.0 M NaCl over the pH range from 2.5 to 8.2 with variable concentrations of manganese dioxide from 0.01 mIn the pH range from 2.0 to 3.5, the oxidation of Pu(IV) by manganese dioxide was first order with respect to the concentration of manganese dioxide and −0.21 with respect to the hydrogen ion concentration. Consequently, assuming a first order dependence with respect to the concentration of Pu(IV), the oxidation reaction can be described by the following rate equation:with

Horseradish peroxidase. XXXII. pH dependence of the oxidation of L-(−)-tyrosine by compound I

1978 ◽  
Vol 56 (12) ◽  
pp. 1115-1119 ◽  
Author(s):  
I. Ralston ◽  
H. B. Dunford
Keyword(s):  
Horseradish Peroxidase ◽  
Ph Dependence ◽  
Nonlinear Least Squares ◽  
Compound I ◽  
Ph Profile ◽  
Rate Versus ◽  
Tyrosine Oxidation ◽  
Phenolic Group ◽  
Ph Range ◽  
Single Enzyme

The rate of oxidation of L-(−)-tyrosine by horseradish peroxidase compound I has been studied as a function of pH at 25 °C and ionic strength 0.11. Over the pH range of 3.20–11.23 major effects of three ionizations were observed. The pKa values of the phenolic (pKa = 10.10) and amino (pKa = 9.21) dissociations of tyrosine and a single enzyme ionization (pKa = 5.42) were determined from nonlinear least squares analysis of the log rate versus pH profile. It was noted that the less acidic form of the enzyme was most reactive; hence, the reaction is described as base catalyzed. The rate of tyrosine oxidation falls rapidly with the deprotonation of the phenolic group.

Oxidation of Nickel(II) and Manganese(II) by Peroxodisulfate in Aqueous Solution in the Presence of Molybdate. Crystal Structure of the (NH4)6[NiMo9O32].6H2O Product

1992 ◽  
Vol 45 (12) ◽  
pp. 1943 ◽  
Author(s):  
SJ Dunne ◽  
RC Burns ◽  
GA Lawrance
Keyword(s):  
Rate Constant ◽  
Linear Dependence ◽  
Ph Dependence ◽  
Order Rate Constant ◽  
X Ray Diffraction ◽  
X Ray ◽  
First Order ◽  
Oxidant Concentration ◽  
Ph Range ◽  
Kinetics Of

Oxidation of Ni2+,aq, by S2O82- to nickel(IV) in the presence of molybdate ion, as in the analogous manganese system, involves the formation of the soluble heteropolymolybdate anion [MMogO32]2- (M = Ni, Mn ). The nickel(IV) product crystallized as (NH4)6 [NiMogO32].6H2O from the reaction mixture in the rhombohedra1 space group R3, a 15.922(1), c 12.406(1) � ; the structure was determined by X-ray diffraction methods, and refined to a residual of 0.025 for 1741 independent 'observed' reflections. The kinetics of the oxidation were examined at 80 C over the pH range 3.0-5.2; a linear dependence on [S2O82-] and a non-linear dependence on l/[H+] were observed. The influence of variation of the Ni/Mo ratio between 1:10 and 1:25 on the observed rate constant was very small at pH 4.5, a result supporting the view that the precursor exists as the known [NiMo6O24H6]4- or a close analogue in solution. The pH dependence of the observed rate constant at a fixed oxidant concentration (0.025 mol dm-3) fits dequately to the expression kobs = kH [H+]/(Ka+[H+]) where kH = 0.0013 dm3 mol-1 s-1 and Ka = 4-0x10-5. The first-order dependence on peroxodisulfate subsequently yields a second-order rate constant of 0.042 dm3 mol-1 s-1. Under analogous conditions, oxidation of manganese(II) occurs eightfold more slowly than oxidation of nickel(II), whereas oxidation of manganese(II) by peroxomonosulfuric acid is 16-fold faster than oxidation by peroxodisulfate under similar conditions.

Mechanistic Information from the Effect of Pressure on the Kinetics of Hydrolysis of Iodopentaaquochromium(III) Ion

1975 ◽  
Vol 53 (24) ◽  
pp. 3697-3701 ◽  
Author(s):  
Milton Cornelius Weekes ◽  
Thomas Wilson Swaddle
Keyword(s):  
Ionic Strength ◽  
Hydrogen Ion ◽  
Ion Concentration ◽  
Hydrogen Ion Concentration ◽  
Kinetics Of Hydrolysis ◽  
Rate Of Hydrolysis ◽  
Kinetics Of ◽  
Hydrolysis Of ◽  
Aqueous Hclo ◽  
Conjugate Base

The rate of hydrolysis of iodopentaaquochromium(III) ion has been measured as a function of pressure (0.1 to 250 MPa) and hydrogen ion concentration (0.1 to 1.0 mol kg−1) at 298.2 K and ionic strength 1.0 mol kg−1 (aqueous HClO4–LiClO4). The volumes of activation for the acid independent and inversely acid dependent hydrolysis pathways are −5.4 ± 0.5 and −1.6 ± 0.3 cm3 mol−1 respectively, and are not detectably pressure-dependent. Consideration of these values, together with the molar volume change of −3.3 ± 0.3 cm3 mol−1 determined dilatometrically for the completed hydrolysis reaction, indicates that the mechanisms of the two pathways are associative interchange (Ia) and dissociative conjugate base (Dcb) respectively.

Sign in / Sign up

Export Citation Format

Share Document