scholarly journals Analysis of the optical absorption and magnetic-circular-dichroism spectra of peanut peroxidase: electronic structure of a peroxidase with biochemical properties similar to those of horseradish peroxidase

1994 ◽  
Vol 301 (2) ◽  
pp. 335-341 ◽  
Author(s):  
M J Rodríguez Marañón ◽  
D Mercier ◽  
R B van Huystee ◽  
M J Stillman
Keyword(s):  
Electronic Structure ◽  
Horseradish Peroxidase ◽  
Optical Absorption ◽  
Spectral Data ◽  
Electronic Structures ◽  
General Mechanism ◽  
Compound I ◽  
Plant Peroxidases ◽  
Compound Ii ◽  
Peanut Peroxidase

The electronic structures of the cationic isoenzyme of peanut peroxidase, horseradish peroxidase (isoenzyme C) and bovine liver catalase are compared through analysis of their optical absorption and magnetic c.d. (m.c.d.) spectral properties. The spectral data for the native resting states and compounds I and II of peanut peroxidase (PeP) are reported. The absorption and m.c.d. data for the native PeP exhibit bands characteristic of the high-spin ferric haem. The absorption spectrum of PeP compound I closely resembles that observed for the HRP compound I species. The m.c.d. data for PeP I clearly identifies that ring oxidation has occurred. One-electron reduction forms the PeP compound II species. The absorption and m.c.d. spectra recorded for PeP II exhibit the well-resolved spectral characteristics previously observed for both HRP compound II and catalase compound II. The spectral data of PeP with HRP and catalase are compared. The data clearly indicate that the m.c.d. spectral patterns of both plant peroxidases (PeP and HRP) are very similar and, therefore, the electronic structures of their resting states, and as well their primary and secondary compounds, must be similar. The m.c.d. data suggest that, while the compound I species of PeP and HRP belong to one electronic class, catalase compound I belongs to a different class. These data emphasize how the ground states of these two classes of oxidized haem, may be characterized as predominantly 2A2u (PeP I and HRP I) or 2A1u (catalase I). Peanut peroxidase is the second plant peroxidase for which the electronic structure of the compound I intermediate has been studied using the m.c.d. technique. The similarities with horseradish peroxidase allow us to suggest that plant peroxidases may operate by the same general mechanism, in spite of the low degree of sequence similarity between their polypeptide chains.

Titration Study of Guaiarcol Oxidation by Horseradish Peroxidase

1975 ◽  
Vol 53 (6) ◽  
pp. 649-657 ◽  
Author(s):  
Marius Santimone
Keyword(s):  
Hydrogen Peroxide ◽  
Electron Transfer ◽  
Low Temperature ◽  
Horseradish Peroxidase ◽  
Catalytic Amount ◽  
Reaction Scheme ◽  
General Mechanism ◽  
Compound I ◽  
Compound Ii ◽  
Titration Study

Titration of guaiacol by hydrogen peroxide in the presence of a catalytic amount of horseradish peroxidase shows that the reduction of hydrogen peroxide proceeds by the abstraction of two electrons from a guaiacol molecule. In the same way, it can be demonstrated that 0.5 mol of guaiacol can reduce, at low temperature, 1 mol of peroxidase compound I to compound II. Moreover, the reaction between equal amounts of compound I and guaiacol at low temperature produces the native enzyme. A reaction scheme is proposed which postulates that two electrons are transferred from guaiacol to compound I giving ferriperoxidase and oxidized guaiacol with the intermediary formation of compound II. The direct two-electron transfer from guaiacol to compound I without a dismutation of product free radicals must be considered as an exception to the general mechanism involving a single-electron transfer.

Rate constants for reactions of horseradish peroxidase compounds I and II with 4-substituted arylboronic acids

1994 ◽  
Vol 72 (10) ◽  
pp. 2159-2162 ◽  
Author(s):  
Weimei Sun ◽  
Xiaoying Ji ◽  
Larry J. Kricka ◽  
H. Brian Dunford
Keyword(s):  
Horseradish Peroxidase ◽  
Rate Constants ◽  
Compound I ◽  
Arylboronic Acid ◽  
Experimental Conditions ◽  
Kinetic Measurements ◽  
Arylboronic Acids ◽  
Total Ionic Strength ◽  
Compound Ii ◽  
Catalyzed Oxidation

The rate constants for the reactions of horseradish peroxidase compound I (k1) and compound II (k2) with three 4-substituted arylboronic acids, which enhance chemiluminescence in the horseradish peroxidase catalyzed oxidation of luminol by hydrogen peroxide, were determined at pH 8.6, total ionic strength 0.11 M, using stopped-flow kinetic measurements. For comparison, the rate constants of the reactions of 4-iodophenol with compounds I and II were also determined under the same experimental conditions. The three arylboronic acid derivatives and their rate constants are: 4-biphenylboronic acid, k1 = (1.21 ± 0.08) × 106 M−1 s−1, k2 = (4.6 ± 0.2) × 105 M−1 s−1; 4-bromophenylboronic acid, k1 = (5.5 ± 0.2) × 104 M−1 s−1, k2 = (3.6 ± 0.2) × 104 M−1 s−1; and 4-iodophenylboronic acid, k1 = (1.1 ± 0.2) × 105 M−1 s−1, k2 = (1.3 ± 0.1) × 104 M−1 s−1. 4-Biphenylboronic acid, which shows comparable luminescent enhancement to 4-iodophenol, has the highest reactivity in the reduction of both compounds I and II among the three arylboronic acid derivatives tested.

Electronic Structure and Optical Properties of ZnO with Antisite Defects

2013 ◽  
Vol 341-342 ◽  
pp. 301-306
Author(s):  
X.J. Xie ◽  
W.H. Wang ◽  
L.Y. Li ◽  
X.G. Luo ◽  
Y.H. Cheng
Keyword(s):  
Optical Properties ◽  
Electronic Structure ◽  
Optical Absorption ◽  
Electronic Structures ◽  
Low Energy ◽  
Visible Light Region ◽  
Optical Absorption Edge ◽  
Light Region ◽  
Level Shifts ◽  
Antisite Defects

We investigate the electronic structures and optical properties of ZnO with antisite defects OZn using the density function pseudopotential method. Our results show that the Fermi level shifts into the conduction band after introducing one or two OZn defects into ZnO supercell, indicating that the system displays a metallic-like characteristic. Moreover, the antisite defects lead to a redshift of the optical absorption edge and obvious optical absorption in the visible light region. Especially, the optical properties are influenced by the configurations of two OZn defects in our considered ZnO supercell. The strongest optical absorption occurs when the two defects are connected by-Zn-O-Zn-bond in the ab plane. These findings are possibly applicable for designing new optoelectronic and photoelectrochemical devices with improved low energy light absorption.

scholarly journals Scavenging of oxygen radicals by heme peroxidases.

1996 ◽  
Vol 43 (4) ◽  
pp. 673-678 ◽  
Author(s):  
L Gebicka ◽  
J L Gebicki
Keyword(s):  
Horseradish Peroxidase ◽  
Hydroxyl Radicals ◽  
Superoxide Radical ◽  
Cation Radical ◽  
Compound I ◽  
Superoxide Radical Anion ◽  
Form Compound ◽  
Activity Loss ◽  
Heme Peroxidases ◽  
Compound Ii

The reactions of two heme peroxidases, horseradish peroxidase and lactoperoxidase and their compounds II (oxoferryl heme intermediates, Fe(IV) = O or ferric protein radical Fe(III)R.) and compounds III (resonance hybrids [Fe(III)-O2-. Fe(II)-O2] with superoxide radical anion generated enzymatically or radiolytically, and with hydroxyl radicals generated radiolytically, were investigated. It is suggested that only the protein radical form of compound II of lactoperoxidase reacts with superoxide, whereas compound II of horseradish peroxidase, which exists only in oxoferryl form, is unreactive towards superoxide. Compound III of the investigated peroxidases does not react with superoxide. The lactoperoxidase activity loss induced by hydroxyl radicals is closely related to the loss of the ability to form compound I (oxoferryl porphyrin pi-cation radical, Fe(IV) = O(Por+.) or oxoferryl protein radical Fe(IV) = O(R.)). On the other hand, the modification of horseradish peroxidase induced by hydroxyl radicals has been reported to cause also restrictions in substrate binding (Gebicka, L. & Gebicki, J.L., 1996, Biochimie 78, 62-65). Nevertheless, it has been found that only a small fraction of hydroxyl radicals generated homogeneously does inactivate the enzymes.

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 Mechanism of inhibition of horseradish peroxidase-catalysed iodide oxidation by EDTA

1994 ◽  
Vol 298 (2) ◽  
pp. 281-288 ◽  
Author(s):  
D K Bhattacharyya ◽  
S Adak ◽  
U Bandyopadhyay ◽  
R K Banerjee
Keyword(s):  
Horseradish Peroxidase ◽  
Kinetic Studies ◽  
Spectral Shift ◽  
Spectral Studies ◽  
Isosbestic Point ◽  
Dependent Manner ◽  
Compound I ◽  
Iodide Oxidation ◽  
Hyperfine Splitting Constant ◽  
Compound Ii

EDTA inhibits horseradish peroxidase (HRP)-catalysed iodide oxidation in a concentration and pH-dependent manner. It is more effective at pH 6 than at lower pH values. A plot of log Kiapp. values as a function of pH yields a sigmoidal curve from which a pKa value of 5.4 can be calculated for an ionizable group on the catalytically active HRP for EDTA inhibition. Among the structural analogues of EDTA, tetramethylethylenediamine (TEMED) is 80% as effective as EDTA, whereas the EDTA-Zn2+ chelate and EGTA are ineffective. Kinetic studies indicate that EDTA competitively inhibits iodide oxidation. Spectral studies show that EDTA can quickly reduce compound I to compound II, but reduction of preformed compound II to the native enzyme is relatively slow, as demonstrated by the time-dependent spectral shift from 417 nm to 402 nm through an isosbestic point at 408 nm. Under steady-state conditions, in a reaction mixture containing HRP, EDTA and H2O2, the enzyme remains in the compound-II form, with absorption maxima at 417, 527 and 556 nm. Direct evidence for one-electron oxidation of EDTA by HRP intermediates is provided by the appearance of an e.s.r. signal of a 5,5-dimethyl-1-pyrroline N-oxide (spin trap)-EDTA radical adduct [aN (hyperfine splitting constant) = 1.5 mT] in e.s.r. studies. The signal intensity, however, decreases in the presence of iodide. The KD of the HRP-EDTA complex obtained from optical difference spectroscopy increases with an increase in iodide concentration, and the double-reciprocal plot for EDTA binding indicates that EDTA and iodide compete for the same binding site for oxidation. We suggest that EDTA inhibits iodide oxidation by acting as an electron donor.

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.

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