Horseradish Peroxidase. XVIII. The Arrhenius Activation Energy for the Formation of Compound I

Hewson, W D; Dunford, H. Brian

doi:10.1139/v75-268

Cited by 34 publications

(16 citation statements)

References 8 publications

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“…The apparent second-order rate constant we obtained, (1.8 ± 0.1) X 107 M-1 s-1, is comparable to values previously reported: (1.0 ± 0.2) X 107 M~'s-1 for rat chloroma peroxidase (Newton et al, 1965); 2.0 X 107 M-1 s-1 for canine pus myeloperoxidase (Harrison, 1976); and 2.3 X 107 M-1 s_1 for human granulocyte myeloperoxidase (Bolscher & Wever, 1984). The rate of myeloperoxidase compound I formation is also the same as that for compound I formation of horseradish peroxidase (Hewson & Dunford, 1975).…”

Section: Time (Min)supporting

confidence: 65%

Spectral and Kinetic Studies on the Formation of Myeloperoxidase Compounds I and II: Roles of Hydrogen Peroxide and Superoxide

Marquez

Huang²,

Dunford³

1994

Biochemistry

141

145

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The conversion of myeloperoxidase to compounds I and II in the presence of H2O2 has been reinvestigated in order to explain the abnormal stoichiometry of compound I formation and the fast spontaneous decay of compound I to compound II. Rapid-scan studies show that at least a 20-fold excess of H2O2 is required to obtain a good spectrum of relatively pure compound I; a further increase in H2O2 concentration causes compound I to be reduced to compound II, which is a very stable intermediate. Compound I formation is reversible, with an apparent second-order forward rate constant of (1.8 +/- 0.1) x 10(7) M-1 s-1 and a reverse rate constant of 58 +/- 4 s-1, giving a constant of 3.2 microM for the dissociation of compound I to native enzyme and H2O. This reversibility is one factor that can explain the large excess of H2O2 required to form compound I. The apparent second-order rate constant for compound II formation from compound I and H2O2 is (8.2 +/- 0.2) x 10(4) M-1 s-1. We confirm pH dependence studies, which suggest that the formation of compounds I and II is controlled by a residue in the enzyme with a pKa of about 4.0. Excess H2O2 is also converted to O2 via catalase activity of the enzyme. However, we do not consider this a dominant pathway because it fails to account for the fast spontaneous reduction of compound I to compound II. The time courses for both the decay of compound I and the formation of compound II are biphasic.(ABSTRACT TRUNCATED AT 250 WORDS)

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Section: Time (Min)supporting

confidence: 65%

Spectral and Kinetic Studies on the Formation of Myeloperoxidase Compounds I and II: Roles of Hydrogen Peroxide and Superoxide

Marquez

Huang²,

Dunford³

1994

Biochemistry

141

145

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“…Compound I Formation Rate and Effect of Chelators. The primary reaction product of peroxidases with H2O2 is the oxidized intermediate compound I. MnP compound I is similar to other peroxidase compounds I in its spectral features and in the activation energy for its formation (Wariishi et al, 1988(Wariishi et al, ,1989Dunford & Stillman, 1976;Renganathan & Gold, 1986;Marquez et al, 1988;Hewson & Dunford, 1975;Andrawis et al, 1988;Job etal., 1978). We have shown that the second-order rate constant for MnP compound I formation with H2O2 as the substrate is independent of pH over the range 3.1-8.3 (Wariishi et al, 1989).…”

Section: Discussionmentioning

confidence: 92%

Mechanism of Manganese Peroxidase Compound II Reduction. Effect of Organic Acid Chelators and pH

Kishi¹,

Wariishi²,

Marquez³

et al. 1994

Biochemistry

122

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The effect of oxalate, malonate, lactate, and succinate chelators on the reduction of Phanerochaete chrysosporium manganese peroxidase compound II by MnII was investigated using stopped-flow techniques. All rate data were collected from single-turnover experiments under pseudo-first-order conditions. With oxalate, the reduction of compound II by MnII exhibited saturation behavior when the observed pseudo-first-order rate constants were plotted against oxalate concentration. The plots passed through the origin, indicating that the reduction by MnII is irreversible at all concentrations of oxalate. Maximal stimulation of the rate of compound II reduction occurred at 2 mM oxalate, the concentration of oxalate found in the extracellular medium of agitated cultures of this fungus. In contrast, maximal stimulation of the reduction of compound II by MnII only was observed at high (> 20 mM) nonphysiological concentrations of malonate and lactate. Furthermore, at low concentrations of malonate and lactate, the reduction of compound II appeared to be reversible. These results suggest that at physiological concentrations oxalate chelates and stabilizes MnIII, enhancing its efficient removal from the enzyme. The rate constants for compound II reduction exhibited bell-shaped curves as a function of pH and had optima at pHs 5.0-5.4. In the presence of succinate, triphasic kinetics were observed for compound II reduction by MnII. In contrast to the reduction of compound II by MnII, various chelators had no observable effect on the formation of compound I. However, they did affect the steady-state oxidation of 2,6-dimethoxyphenol.

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“…The apparent activation energy for the formation of compound I of native HRP has been reported to be 14.7 ± 4.2 kJ mol Ϫ1 . 30 The corresponding energy for the formation of MnHRP᎐I is slightly higher for all the peroxides (see Table 2). The minimum theoretical energy of activation for a reaction in water (E act water ) has been found to be 16.3 kJ mol Ϫ1 , 31 which is lower than the energy of activation reported for the formation of HRP᎐I.…”

Section: Discussionmentioning

confidence: 95%

Kinetics and thermodynamics of the reaction of peroxides with manganese-reconstituted horseradish peroxidase: a stopped-flow transient kinetic investigation

Khan¹,

Mondal²,

Mitra³

1998

J. Chem. Soc., Dalton Trans.

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Horseradish Peroxidase. XVIII. The Arrhenius Activation Energy for the Formation of Compound I

Cited by 34 publications

References 8 publications

Spectral and Kinetic Studies on the Formation of Myeloperoxidase Compounds I and II: Roles of Hydrogen Peroxide and Superoxide

Spectral and Kinetic Studies on the Formation of Myeloperoxidase Compounds I and II: Roles of Hydrogen Peroxide and Superoxide

Mechanism of Manganese Peroxidase Compound II Reduction. Effect of Organic Acid Chelators and pH

Kinetics and thermodynamics of the reaction of peroxides with manganese-reconstituted horseradish peroxidase: a stopped-flow transient kinetic investigation

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