Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:1.11.1.7 (peroxidase)
65,474 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Lignin peroxidase (LiP) from the white rot fungus Phanerochaete chrysosporium catalyzes the H2O2-dependent oxidation of veratryl alcohol (VA), a secondary metabolite of the fungus, to veratryl aldehyde (VAD). The oxidation of VA does not seem to be simply one-electron oxidation by LiP compound I (LiPI) to its cation radical (VA.+) and the second by LiP compound II (LiPII) to VAD. Moreover, the rate constant for LiPI reduction by VA (3 x 10(5) M-1 s-1) is certainly sufficient, but the rate constant for LiPII reduction by VA (5.0 +/- 0.2 s-1) is insufficient to account for the turnover rate of LiP (8 +/- 0.4 s-1) at pH 4.5. Oxalate was found to decrease the turnover rate of LiP to 5 s-1, but it had no effect on the rate constants for LiP with H2O2 or LiPI and LiPII, the latter formed by reduction of LiPI with ferrocyanide, with VA. However, when LiPII was formed by reduction of LiPI with VA, an oxalate-sensitive burst phase was observed during its reduction with VA. This was explained by the presence of LiPII, formed by reduction of LiPI with VA, in two different states, one that reacted faster with VA than the other. Activity during the burst was sensitive to preincubation of LiPI with VA, decaying with a half-life of 0.54 s, and was possibly due to an unstable intermediate complex of VA.+ and LiPII. This was supported by an anomalous, oxalate-sensitive, LiPII visible absorption spectrum observed during steady state oxidation of VA. The first order rate constant for the burst phase was 8.3 +/- 0.2 s-1, fast enough to account for the steady state turnover rate of LiP at pH 4.5. Thus, it was concluded that oxalate decreased the turnover of LiP by reacting with VA.+ bound to LiPII. The VA.+ concentration measured by electron spin resonance spectroscopy (ESR) was 2.2 microM at steady state (10 microM LiP, 250 microM H2O2, and 2 mM VA) and increased to 8.9 microM when measured after the reaction was acid quenched. Therefore, we assumed the presence of two states of VA.+ bound to LiPII, one ESR-active and one ESR-silent. The ESR-silent species, which could be detected after acid quenching, would be responsible for the burst phase. Both of the VA.+ species disappeared in the presence of 5 mM oxalate. The ESR-active species reached a maximum (3.5 microM) at 0.5 mM VA under steady state. From these studies, a mechanism for VA oxidation by LiP is proposed in which a complex of LiPII and VA.+ reacts with an additional molecule of VA, leading to veratryl aldehyde formation.
...
PMID:Veratryl alcohol oxidation by lignin peroxidase. 852 62

Lignin peroxidase (LiP) catalyzes the H2O2-dependent oxidation of veratryl alcohol (VA) to veratryl aldehyde, with the enzyme-bound veratryl alcohol cation radical (VA.+) as an intermediate [Khindaria et al. (1995) Biochemistry 34, 16860-16869]. The decay constant we observed for the enzyme generated cation radical did not agree with the decay constant in the literature [Candeias and Harvey (1995) J. Biol. Chem. 270, 16745-16748] for the chemically generated radical. Moreover, we have found that the chemically generated VA.+ formed by oxidation of VA by Ce(IV) decayed rapidly with a first-order mechanism in air- or oxygen-saturated solutions, with a decay constant of 1.2 x 10(3) s-1, and with a second-order mechanism in argon-saturated solution. The first-order decay constant was pH- independent suggesting that the rate-limiting step in the decay was deprotonation. When VA.+ was generated by oxidation with LiP the decay also occurred with a first-order mechanism but was much slower, 1.85 s-1, and was the same in both oxygen- and argon-saturated reaction mixtures. However, when the enzymatic reaction mixture was acid-quenched the decay constant of VA.+ was close to the one obtained in the Ce(IV) oxidation system, 9.7 x 10(2) s-1. This strongly suggested that the LiP-bound VA.+ was stabilized and decayed more slowly than free VA.+. We propose that the stabilization of VA.+ may be due to the acidic microenvironment in the enzyme active site, which prevents deprotonation of the radical and subsequent reaction with oxygen. We have also obtained reversible redox potential of VA.+/VA couple using cyclic voltammetery. Due to the instability of VA.+ in aqueous solution the reversible redox potential was measured in acetone, and was 1.36 V vs normal hydrogen electrode. Our data allow us to propose that enzymatically generated VA.+ can act as a redox mediator but not as a diffusible oxidant for LiP-catalyzed lignin or pollutant degradation.
...
PMID:Stabilization of the veratryl alcohol cation radical by lignin peroxidase. 863 88

Lignin peroxidase is generally considered to be a primary catalyst for oxidative depolymerization of lignin by white-rot fungi. However, some white-rot fungi lack lignin peroxidase. Instead, many produce laccase, even though the redox potentials of known laccases are too low to directly oxidize the non-phenolic components of lignin. Pycnoporus cinnabarinus is one example of a laccase-producing fungus that degrades lignin very efficiently. To overcome the redox potential barrier, P. cinnabarinus produces a metabolite, 3-hydroxyanthranilate that can mediate the oxidation of how non-phenolic substrates by laccase. This is the first description of how laccase might function in a biological system for the complete depolymerization of lignin.
...
PMID:A fungal metabolite mediates degradation of non-phenolic lignin structures and synthetic lignin by laccase. 870 3

Lignin peroxidase-like genes were PCR amplified from Phanerochaete sordida and Ceriporiopsis subvermispora, fungi lacking lignin peroxidase (LiP) activity. Amplification products were highly similar to previously described LiP genes. Using reverse transcription-coupled PCR a LiP-like cDNA clone was amplified from P. sordida RNA. In contrast, no evidence was obtained for transcription of C. subvermispora LiP genes.
...
PMID:Lip-like genes in Phanerochaete sordida and Ceriporiopsis subvermispora, white rot fungi with no detectable lignin peroxidase activity. 877 5

Lignin peroxidase (LiP) isozymes of Phanerochaete chrysosporium are encoded by a large family of closely related genes, whose total number is still unknown. Among genomic clones, obtained using the polymerase chain reaction to clone the LiP gene LPOA from Phanerochaete chrysosporium strain BKM-F 1767, another LiP gene was found. This gene, HG3, showed more than 95% nucleotide homology to those LiP gene variants which encode LiP isozyme H8. The gene encodes a protein of 372 amino acids, including the typical leader sequence for secretion, that is identical to the LiP isozyme H8 except for 6 amino acid substitutions.
...
PMID:Cloning and characterization of another lignin peroxidase gene from the white-rot fungus Phanerochaete chrysosporium. 883 87

Lignin peroxidase (LiP) from Phanerochaete chrysosporium catalyzes the H2O2 dependent one- and two-electron oxidations of substrates. The catalytic cycle involves the oxidation of ferric-LiP by H2O2 by two electrons to compound I, which is an oxoferryl heme and a free radical. It has been speculated that the unpaired electron is in a pi delocalized porphyrin radical. However, no direct evidence for the presence of the free radical has been reported. We present electron paramagnetic resonance (EPR) detection and characterization of compound I of LiP. The LiP compound I EPR signal is different than those reported previously for compound I of horseradish peroxidase and chloroperoxidase. However, the EPR signal of compound I of LiP (axial g tensor extending from gperpendicular = 3.42 to gparallel approximately 2) is very similar to the EPR signals of compound I of ascorbate peroxidase and catalase from Micrococcus lysodeikticus, in which the radical has been identified as a porphyrin pi-cation radical. On the basis of the analysis of our data and comparison with the earlier published results for compounds I of other peroxidases, we interpret the LiP compound I signal by a model for exchange coupling between an S = 1 oxyferryl [Fe = O]2+ moiety and a porphyrin pi-cation radical (S = 1/2) [Schulz, C.E., et al. (1979) FEBS Lett. 103, 102-105]. The exchange coupling is characterized by ferromagnetic rather than an antiferromagnetic interaction between the two species. The ferric-Lip EPR signal suggests that the iron in the heme is in near perfect orthogonal symmetry and provides additional evidence of the ferromagnetic interaction between the oxoferryl iron center and the porphyrin pi-cation radical.
...
PMID:EPR detection and characterization of lignin peroxidase porphyrin pi-cation radical. 885 47

Azide ion is a mechanism-based inactivator of horseradish peroxidase [Ortiz de Montellano et al. (1988) Biochemistry 27, 5470-5476] and the peroxidase from the coprophilic fungus Coprinus macrorhizus [DePillis and Ortiz de Montellano (1989) Biochemistry 28, 7947-7952]. These peroxidases mediate the one-electron oxidation of azide ion-forming azidyl radical. Inactivation of these enzymes is caused by covalent modification of the heme prosthetic groups by azidyl radical. Lignin peroxidases from the wood-rotting fungus Phanerochaete chrysosporium are also inactivated when they catalyze oxidation of azide ion [Tuisel et al. (1991) Arch. Biochem. Biophys. 288, 456-462; DePillis et al. (1990) Arch. Biochem. Biophys. 280, 217-223]. Following inactivation of horseradish peroxidase and the peroxidase from C. macrorhizus substantial amounts of azidyl-heme adducts have been found. Only trace amounts of such adducts have been found following azide-mediated inactivation of lignin peroxidase. Nevertheless, we have shown that during oxidation of azide by lignin peroxidase H8 destruction of heme occurred and a substantial fraction of the enzyme is irreversibly inactivated. However, the rest of the enzyme forms a relatively stable ferrous-nitric oxide (NO) complex. Although this complex appears to be an inactivated form of the enzyme, we have shown that, when present as the ferrous-NO complex, the enzyme is actually protected from inactivation. The lignin peroxidase ferrous-NO complex reverts slowly (t1/2 = 6.3 x 10(3) s) to the ferric form. Reversion is accelerated if the complex is chromatographed on a PD-10 (Sephadex G-25) column or if veratryl alcohol is added. If azide and hydrogen peroxide (a required cosubstrate) are present (or added), the enzyme undergoes another cycle of catalysis and further inactivation. A detailed reaction mechanism is proposed that is consistent with our experimental observations, the chemistry of azide, and our current understanding of peroxidases.
...
PMID:Further studies on the inactivation by sodium azide of lignin peroxidase from Phanerochaete chrysosporium. 905 50

The lignin biodegradation process has an important role in the carbon cycle of the biosphere. The study of this natural process has developed mainly with the use of basidiomycetes in laboratory investigations. This has been a logical approach since most of the microorganisms involved in lignocellulosic degradation belong to this class of fungi. However, other microorganisms such as ascomycetes and also some bacteria, are involved in the lignin decaying process. This work focuses on lignin biodegradation by a microorganism belonging to the ascomycete class, Chrysonilia sitophila. Lignin peroxidase production and characterization, mechanisms of lignin degradation (lignin model compounds and lignin in wood matrix) and biosynthesis of veratryl alcohol are outstanding. Applications of C. sitophila for effluent treatment, wood biodegradation and single-cell protein production are also discussed.
...
PMID:Lignin biodegradation by the ascomycete Chrysonilia sitophila. 917 Feb 55

Lignin peroxidases (LiP) from the white-rot fungus Phanerochaete chrysosporium oxidize veratryl alcohol (VA) by two electrons to veratryl aldehyde, although the VA cation radical (VA.+) is an intermediate [Khindaria, A., et al. (1995) Biochemistry 34, 6020-6025]. It was speculated, on the basis of kinetic evidence, that VA*+ can form a catalytic complex with LiP compound II. We have used low-temperature EPR to provide direct evidence for the formation of the complex. The EPR spectrum of VA*+ obtained at 4 K was explained by a model for coupling between the oxoferryl moiety of the heme (S = 1) and VA.+ (S = 1/2) similar to the model proposed for an oxyferryl and a porphyrin pi cation radical of horseradish peroxidase. The coupling constant suggested that VA.+ was equally ferro- and antiferromagnetically coupled to the oxoferryl moiety. The spectrum was simulated with g perpendicular only marginally greater than g parallel. This was surprising since the only other known organic radical coupled to the heme iron in a peroxidase is the tryptophan cation radical in cytochrome c peroxidase which exhibits a g tensor with g parallel greater than g perpendicular. Spin concentration analysis suggested that the 1 mol of VA*+ was coupled to the oxoferryl moiety per mole of enzyme. The VA.+ signal decayed with a first-order decay constant of 1.76 s-1, in close agreement with the earlier published decay constant of 1.85 s-1 from room-temperature EPR studies. The exchange coupling between VA.+ and the oxoferryl moiety strongly advocates calling this species (VA.+ and LiP compound II) a catalytic complex.
...
PMID:Detection and characterization of the lignin peroxidase compound II-veratryl alcohol cation radical complex. 936 91

Lignin peroxidase (LiP) from Phanerochaete chrysosporium catalyzes irreversible oxidative damage to ferricytochrome c (Cc3+) in the presence of H2O2 and 3,4-dimethoxybenzyl (veratryl) alcohol (VA). Atomic absorption analysis and UV/vis spectroscopy indicate that the oxidation of Cc3+ is accompanied by a loss of heme iron from the protein and probably oxidation of the porphyrin ring. At H2O2 concentrations of 7.5 microM or higher, this oxidation of Cc3+ by LiP is strictly dependent on the presence of VA. The latter is not oxidized to veratraldehyde at a significant rate in the presence of either ferrocytochrome c (Cc2+) or Cc3+, indicating it is not stimulating the reactions by specifically reducing LiP compound II. LiP is inactivated rapidly in 100 microM H2O2, and the presence of 500 microM VA protects LiP from this inactivation. Neither 20 microM Cc3+ nor 20 microM VA alone can protect LiP from inactivation; however, 20 microM each of VA and Cc3+ together protect LiP fully. This and other results strongly suggest that VA is acting as a protein-bound redox mediator in the oxidation of Cc3+. SDS-PAGE analysis of the Cc3+ oxidation products demonstrates the formation of some covalently linked dimer of Cc3+ in addition to the oxidized Cc3+ monomer. Amino acid analysis of the dimeric and monomeric products indicates the presence of oxidized Met and Tyr residues. This suggests that Tyr residues on the surface of the protein are oxidized to Tyr radicals during LiP oxidation and that some of these radicals subsequently undergo intermolecular radical coupling, resulting in dimerization of some of the Cc3+ molecules. However, most of the Cc3+ molecules appear to be irreversibly oxidized without dimerization. These results demonstrate that Cc3+ can serve as a useful polymeric model of the lignin substrate in studying the enzymatic mechanism of lignin oxidation and the role of VA in the reaction.
...
PMID:Irreversible oxidation of ferricytochrome c by lignin peroxidase. 948 29


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---