On the molecular mechanism of lactoperoxidase-catalyzed H2O2 metabolism and irreversible enzyme inactivation.

Jenzer, Herbert; Jones, Warren C. Jun.; Köhler, H.

doi:10.1016/s0021-9258(18)66749-3

Cited by 57 publications

(11 citation statements)

References 45 publications

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“…In a few seconds et al, 1986). The positions of the Soret bands (λ max ) for the various enzymatic species found here agree very well with those reported in the literature (Jenzer et al, 1986;Courtin et al,1982). Differential Pulse Voltammetry.…”

Section: Methodssupporting

confidence: 90%

Oxidation of Phenolic Compounds by Lactoperoxidase. Evidence for the Presence of a Low-Potential Compound II during Catalytic Turnover

Monzani

Profumo

et al. 1997

Biochemistry

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The lactoperoxidase (LPO)-catalyzed oxidation of p-phenols by hydrogen peroxide has been studied. The behavior of the enzyme differs from that of other peroxidases in this reaction. In particular LPO shows several catalytic intermediates during the catalytic cycle because of its capability to delocalize an oxidizing equivalent on a protein amino acid residue. In the phenol oxidation the enzyme Compound I species, containing an iron-oxo and a protein radical, uses the iron-oxo group at acidic pH and the protein radical in neutral or basic medium. Kinetic and spectroscopic studies indicate that the ionization state of an amino acid residue with pKa 5.8 +/- 0.2, probably the distal histidine, controls the enzyme intermediate forms at different pH. LPO undergoes inactivation during the oxidation of phenols. The inactivation is reversible and depends on the easy formation of Compound III even at low oxidant concentration. The inactivation is due to the substrate redox potential since the best substrate is that with lowest redox potential, while the worst substrate has the highest potential. This strongly indicates that Compound II, formed during catalytic turnover, has a low redox potential, making easier its oxidation by hydrogen peroxide to Compound III. The dependence of LPO activity on the phenols redox potential suggests that the protein radical where an oxidizing equivalent can be localized is a tyrosyl residue.

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Section: Methodssupporting

confidence: 90%

Oxidation of Phenolic Compounds by Lactoperoxidase. Evidence for the Presence of a Low-Potential Compound II during Catalytic Turnover

Monzani

Profumo

et al. 1997

Biochemistry

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“…Experiments for the Detection of Hydrogen Peroxide during the Catalytic Cycle. The presence of hydrogen peroxide in the reaction mixture was analyzed by using the iodimetric assay based on I 3 - , which has a characteristic absorption band at 353 nm (ε 26 000 M -1 cm -1 in water) . When a solution of methanol/aqueous phosphate buffer (50 mM), pH 5.1, 30:1 (v/v), saturated with potassium iodide and atmospheric oxygen is stirred, the I 3 - band develops very slowly.…”

Section: Methodsmentioning

confidence: 99%

Mechanistic, Structural, and Spectroscopic Studies on the Catecholase Activity of a Dinuclear Copper Complex by Dioxygen

Monzani¹,

Battaini²,

Perotti³

et al. 1999

Inorg. Chem.

146

111

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Dinuclear copper(II) complexes with the new ligand 1,6-bis[[bis(1-methyl-2-benzimidazolyl)methyl]amino]-n-hexane (EBA) have been synthesized, and their reactivity as models for tyrosinase has been investigated in comparison with that of previously reported dinuclear complexes containing similar aminobis(benzimidazole) donor groups. The complex [Cu2(EBA)(H2O)4]4+, five-coordinated SPY, with three nitrogen donors from the ligand and two water molecules per copper, can be reversibly converted into the bis(hydroxo) complex [Cu2(EBA)(OH)2]2+ by addition of base (pK a1 = 7.77, pK a2 = 9.01). The latter complex can also be obtained by air oxidation of [Cu2(EBA)]2+ in methanol. The X-ray structural characterization of [Cu2(EBA)(OH)2]2+ shows that a double μ-hydroxo bridge is established between the two Cu(II) centers in this complex. The coordination geometry of the coppers is distorted square planar, with two benzimidazole donors and two hydroxo groups in the equatorial plane, and an additional, lengthened and severely distorted axial interaction (∼2.5 Å) with the tertiary amine donor. The small size and the quality of the single crystal as well as the fair loss of crystallinity during data collection required the use of synchrotron radiation at 100 K. [Cu2(EBA)(OH)2][PF6]2: orthorhombic Pca21 space group, a = 22.458(2) Å, b = 10.728(1) Å, c = 19.843(2) Å, R = 0.089. Besides OH-, the [Cu2(EBA)(H2O)4]4+ complex binds azide as a bridging ligand, with the μ-1,3 mode. Azide can also displace μ-OH in [Cu2(EBA)(OH)2]2+ as a bridging ligand. In general, the binding constants indicate that the long alkyl chain of EBA is less easily folded in the structures containing bridging ligands than the m-xylyl residue present in the previously reported dicopper(II) complexes. Electrochemical experiments show that [Cu2(EBA)(H2O)4]4+ undergoes a single, partially chemically reversible, two-electron reduction to the corresponding dicopper(I) congener at positive potential values (E 0‘ = 0.22 V, vs SCE). Interestingly, however, coordination to azide ion makes the reduction process proceed through two separated one-electron steps. The catalytic activity of [Cu2(EBA)(H2O)4]4+ in the oxidation of 3,5-di-tert-butylcatechol has been examined in methanol/aqueous buffer, pH 5.1. The mechanism of the catalytic cycle parallels that of tyrosinase, where no hydrogen peroxide is released and dioxygen is reduced to water. Low-temperature (−80 °C) spectroscopic experiments show that oxygenation of the reduced complex [Cu2(EBA)]2+ does not produce a stable dioxygen adduct and leads to a μ-oxodicopper(II) species in a fast reaction.

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“…58 Ferrous LPO, on the other hand, has absorption maxima at 434 nm (Soret band), 561 and 593 nm. 62,63 This stable Fe(II) species is formed via a transient Fe(II) intermediate with peak maxima at 444, 561, and 593 nm. The rate of this conversion significantly increases with decreasing pH 64, 65 and is accompanied by structural changes from a relatively open, unrestricted pocket to a constrained one, which binds small ligands at lower rates.…”

Section: Impact Of Covalently Bound Heme On the Spectral Propertiesmentioning

confidence: 99%

Heme to protein linkages in mammalian peroxidases: impact on spectroscopic, redox and catalytic properties

et al. 2007

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On the molecular mechanism of lactoperoxidase-catalyzed H2O2 metabolism and irreversible enzyme inactivation.

Cited by 57 publications

References 45 publications

Oxidation of Phenolic Compounds by Lactoperoxidase. Evidence for the Presence of a Low-Potential Compound II during Catalytic Turnover

Oxidation of Phenolic Compounds by Lactoperoxidase. Evidence for the Presence of a Low-Potential Compound II during Catalytic Turnover

Mechanistic, Structural, and Spectroscopic Studies on the Catecholase Activity of a Dinuclear Copper Complex by Dioxygen

Heme to protein linkages in mammalian peroxidases: impact on spectroscopic, redox and catalytic properties

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