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

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

The extracellular lignin peroxidase from the white-rot basidiomycete Phanerochaete chrysosporium is thought to play an important role in lignin biodegradation. However, the majority of lignin-derived preparations actually experience overall polymerization at the hands of the enzyme in vitro. It has now been found that, in the presence of H2O2 at pH 4.0, the monomeric lignin precursor coniferyl alcohol is polymerized quantitatively by a lignin peroxidase preparation which is uncontaminated with MnII-dependent peroxidases. 13C NMR spectrometry of the resulting dehydropolymerisates from 13C-labeled monolignols confirms that the frequencies of different interunit linkages are very similar to those engendered through the action of horseradish peroxidase with H2O2. Indeed, lignin peroxidase does not ultimately seem to be a prerequisite for lignin degradation in vivo, yet its activity can still accelerate the conversion of lignin-derived preparations by P. chrysosporium to CO2. Consequently, lignin peroxidase can provisionally be expected to fulfill two important functions. On the one hand, the enzyme may detoxify lower molecular weight phenolic compounds released from lignins during their fungal decomposition. On the other hand, through the introduction of suitable functional groups, lignin peroxidase could indirectly enhance the susceptibility of macromolecular lignin structures toward depolymerization by another enzyme.
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PMID:Lignin peroxidase: toward a clarification of its role in vivo. 199 22

Stopped-flow techniques were used to investigate the kinetics of the reaction of lignin peroxidase compounds II and III (LiPII and LiPIII) with peroxides. Rate data were obtained from single-turnover experiments under pseudo-first-order conditions. LiPII reacts with H2O2 or peracetic acid (AcOOH) to form a modified LiPIII, designated as LiPIII*, via a biphasic reaction. During the first phase, LiPIII is formed as an intermediate. Kinetic analysis also indicates a LiPII-peroxide complex. The first-order dissociation rate constants for the reaction of LiPII with H2O2 and AcOOH are 7.9 +/- 0.5 and 4.9 +/- 0.6 s-1, respectively. The rate of the H2O2 reaction is approximately 500 times the rate of the comparable reaction with horseradish peroxidase, suggesting it is physiologically significant. The activation energy for the formation of LiPIII is 23 kJ mol-1. During the second phase, the intermediate LiPIII is converted to LiPIII*, confirmed by analyzing the reaction of exogenously prepared LiPIII with peroxides. The second-order rate constants for the reaction of LiPIII with H2O2 and AcOOH are (3.7 +/- 0.2) x 10(2) M-1 s-1 and (2.9 +/- 0.2) x 10(2) M-1 s-1, respectively. The conversion of LiPIII to LiPIII* is reversible; the first-order rate constant for the reverse reaction is approximately (6.6 +/- 0.6) x 10(-2) s-1. The rates of both LiPIII and LiPIII* formation decrease markedly above pH 4.0. The pH dependence of these reactions is controlled by a heme-linked ionizable group of pK alpha congruent to 4.2.
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PMID:Lignin peroxidase compounds II and III. Spectral and kinetic characterization of reactions with peroxides. 216 33

Lignin peroxidase oxidizes non-phenolic substrates by one electron to give aryl-cation-radical intermediates, which react further to give a variety of products. The present study investigated the possibility that other peroxidative and oxidative enzymes known to catalyse one-electron oxidations may also oxidize non-phenolics to cation-radical intermediates and that this ability is related to the redox potential of the substrate. Lignin peroxidase from the fungus Phanerochaete chrysosporium, horseradish peroxidase (HRP) and laccase from the fungus Trametes versicolor were chosen for investigation with methoxybenzenes as a homologous series of substrates. The twelve methoxybenzene congeners have known half-wave potentials that differ by as much as approximately 1 V. Lignin peroxidase oxidized the ten with the lowest half-wave potentials, whereas HRP oxidized the four lowest and laccase oxidized only 1,2,4,5-tetramethoxybenzene, the lowest. E.s.r. spectroscopy showed that this congener is oxidized to its cation radical by all three enzymes. Oxidation in each case gave the same products: 2,5-dimethoxy-p-benzoquinone and 4,5-dimethoxy-o-benzoquinone, in a 4:1 ratio, plus 2 mol of methanol for each 1 mol of substrate. Using HRP-catalysed oxidation, we showed that the quinone oxygen atoms are derived from water. We conclude that the three enzymes affect their substrates similarly, and that whether an aromatic compound is a substrate depends in large part on its redox potential. Furthermore, oxidized lignin peroxidase is clearly a stronger oxidant than oxidized HRP or laccase. Determination of the enzyme kinetic parameters for the methoxybenzene oxidations demonstrated further differences among the enzymes.
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PMID:Comparison of lignin peroxidase, horseradish peroxidase and laccase in the oxidation of methoxybenzenes. 216 14

Resonance Raman (RR) spectra of several compounds III of lignin peroxidase (LiP) have been measured at 90 K with Soret and visible excitation wavelengths. The samples include LiPIIIa (or oxyLiP) prepared by oxygenation of the ferrous enzyme, LiPIIIb generated by reaction of the native ferric enzyme with superoxide, LiPIIIc prepared from native LiP plus H2O2 followed by removal of excess peroxide with catalase, and LiPIII* made by addition of excess H2O2 to the native enzyme. The RR spectra of these four products appear to be similar and, thus, indicate that the environments of these hexacoordinate, low-spin ferriheme species must also be very similar. Nonetheless, the Soret absorption band of LiPIII* is red-shifted by 5 nm from the 414-nm maximum common to LiPIIIa, -b, and -c [Wariishi, H., & Gold, M.H. (1990) J. Biol. Chem. 265, 2070-2077]. Analysis of the iron-porphyrin vibrational frequencies indicates that the electronic structures for the various compounds III are consistent with an FeIIIO2.-formulation. The spectral changes observed between the oxygenated complex and the ferrous heme of lignin peroxidase are similar to those between oxymyoglobin and deoxymyoglobin. The contraction in the core sizes in compound III relative to the native peroxidase is analyzed and compared with that of other heme systems. EPR spectra confirm that the high-spin ferric form of the native enzyme, with an apparent g = 5.83, is converted into the EPR-silent LiPIII* upon addition of excess H2O2. Its magnetic behavior may be explained by anti-ferromagnetic coupling between the low-spin FeIII and the superoxide ligand.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Resonance Raman spectroscopic characterization of compound III of lignin peroxidase. 217 51

Lignin peroxidase compound III (LiPIII) was prepared via three procedures: (a) ferrous LiP + O2 (LiPIIIa), (b) ferric LiP + O2-. (LiPIIIb), and (c) LiP compound II + excess H2O2 followed by treatment with catalase (LiPIIIc). LiPIIIa, b, and c each have a Soret maximum at approximately 414 nm and visible bands at 543 and 578 nm. LiPIIIa, b, and c each slowly reverted to native ferric LiP, releasing stoichiometric amounts of O2-. in the process. Electronic absorption spectra of LiPIII reversion to the native enzyme displayed isosbestic points in the visible region at 470, 525, and 597 nm, suggesting a single-step reversion with no intermediates. The LiPIII reversion reactions obeyed first-order kinetics with rate constants of approximately 1.0 X 10(-3) s-1. In the presence of excess peroxide, at pH 3.0, native LiP, LiPII, and LiPIIIa, b, and c are all converted to a unique oxidized species (LiPIII*) with a spectrum displaying visible bands at 543 and 578 nm, but with a Soret maximum at 419 nm, red-shifted 5 nm from that of LiPIII. LiPIII* is bleached and inactivated in the presence of excess H2O2 via a biphasic process. The fast first phase of this bleaching reaction obeys second-order kinetics, with a rate constant of 1.7 X 10(1) M-1 s-1. Addition of veratryl alcohol to LiPIII* results in its rapid reversion to the native enzyme, via an apparent one-step reaction that obeys second-order kinetics with a rate constant of 3.5 X 10(1) M-1 s-1. Stoichiometric amounts of O2-. are released during this reaction. When this reaction was run under conditions that prevented further reactions, HPLC analysis of the products demonstrated that veratryl alcohol was not oxidized. These results suggest that the binding of veratryl alcohol to LiPIII* displaces O2-., thus returning the enzyme to its native state. In contrast, the addition of veratryl alcohol to LiPIII did not affect the rate of spontaneous reversion of LiPIII to the native enzyme.
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PMID:Lignin peroxidase compound III. Mechanism of formation and decomposition. 229 39

The oxycomplexes (compound III, oxyperoxidase) of two lignin peroxidase isozymes, H1 (pI = 4.7) and H8 (pI = 3.5), were characterized in the present study. After generation of the ferroperoxidase by photochemical reduction with deazoflavin in the presence of EDTA, the oxycomplex is formed by mixing ferroperoxidase with O2. The oxycomplex of isozyme H8 is very stable, with an autoxidation rate at 25 degrees C too slow to measure at pH 3.5 or 7.0. In contrast, the oxycomplex of isozyme H1 has a half-life of 52 min at pH 4.5 and 29 min at pH 7.5 at 25 degrees C. The decay of isozyme H1 oxycomplex follows a single exponential. The half-lives of lignin peroxidase oxycomplexes are much longer than those observed with other peroxidases. The binding of O2 to ferroperoxidase to form the oxycomplex was studied by stopped-flow methods. At 20 degrees C, the second-order rate constants for O2 binding are 2.3 X 10(5) and 8.9 X 10(5) M-1 s-1 for isozyme H1 and 6.2 X 10(4) and 3.5 X 10(5) M-1 s-1 for isozyme H8 at pH 3.6 and pH 6.8, respectively. The dissociation rate constants for the oxycomplex of isozyme H1 (3.8 Z 10(-3) s-1) and isozyme H8 (1.0 X 10(-3) s-1) were measured at pH 3.6 by CO trapping. Thus, the equilibrium constants (K, calculated from kon/koff) for both isozymes H1 (7.0 X 10(7) M-1) and H8 (6.2 X 10(7) M-1) are higher than that of myoglobin (1.9 Z 10(6) M-1).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Characterization of the oxycomplex of lignin peroxidases from Phanerochaete chrysosporium: equilibrium and kinetics studies. 232 40

Two cDNA clones encoding lignin peroxidase isozymes from Phanerochaete chrysosporium have been isolated and characterized. One of the clones, lambda ML-4, encodes isozyme H8 as does the previously reported clone lambda ML-1 [Tien, M. and Tu, C.-P.D. Nature 326 (1987) 520-523; 328, 742]. Our data are consistent with lambda ML-1 and lambda ML-4 being allelic variants. The other clone, lambda ML-5, encodes a homologous isozyme. We have also isolated the genomic clone corresponding to lambda ML-4 cDNA. Conserved residues thought to be essential for peroxidase function were identified in the predicted amino acid sequences of both cDNA clones. Northern blot analyses indicate that these isozymes are expressed during secondary metabolism, appearing on day 4 of growth and increasing on days 5 and 6.
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PMID:Characterization of two lignin peroxidase clones from Phanerochaete chrysosporium. 247 93

Many of the extracellular lignin-degrading peroxidases from the wood-degrading fungus Phanerochaete chrysosporium are phosphorylated. Immunoprecipitation of the extracellular fluid of cultures grown with H2K32PO4 with a polyclonal antibody raised against one of the lignin peroxidase isozymes, H8 (pI 3.5), revealed the incorporation of H2K32PO4 into lignin peroxidases. Analyses of the purified isozymes from labeled cultures by isoelectric focusing showed that, in addition to isozyme H8, lignin peroxidase isozymes H2 (pI 4.4), H6 (pI 3.7), and H10 (pI 3.3) are also phosphorylated. These analyses also showed that lignin peroxidase isozyme H1 (pI 4.7) and manganese-dependent peroxidase isozymes H3 (pI 4.9) and H4 (pI 4.5) are not phosphorylated. Phosphate quantitation indicated the presence of one molecule of phosphate/molecule of enzyme for all of the phosphorylated isozymes. To locate the site of phosphorylation, one-dimensional phosphoamino acid analysis was performed with hydrolyzed 32P-protein. However, phosphotyrosine, phosphoserine, and phosphothreonine could not be identified. Coupled enzyme assays of acid hydrolysate indicated the presence of mannose 6-phosphate as the phosphorylated component on the lignin peroxidase isozymes. Digestion of the isozymes with N-glycanase released the phosphate component, indicating that the mannose 6-phosphate is contained on an asparagine-linked oligosaccharide.
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PMID:Phosphorylation of lignin peroxidases from Phanerochaete chrysosporium. Identification of mannose 6-phosphate. 258 20

The oxidation-reduction potentials of lignin peroxidase isozymes H1, H2, H8, and H10 as well as the Mn-dependent peroxidase isozymes H3 and H4 are reported. The potentiometric titrations involving the ferrous and ferric states of the enzyme had Nernst plots indicating single-electron transfer. The Em7 values of lignin peroxidase isozymes H1, H2, H8, and H10 are -142, -135, -137, and -127 mV versus standard hydrogen electrode, respectively. The Em7 values for the Mn-dependent peroxidase isozymes H3 and H4 are -88 and -93 mV versus standard hydrogen electrode, respectively. The midpoint potential of H1, H8, and H4 remained unchanged in the presence of their respective substrates, veratryl alcohol and Mn(II). The midpoint potential between the ferric and ferrous forms of isozymes H1 and H4 exhibited a pH-dependent change between pH 3.5 and pH 6.5. These results indicate that the reductive half-reaction of the enzymes is the following: ferric peroxidase + le- + H+----ferrous peroxidase. Above pH 6.5, the effect of pH on the midpoint potential is diminished and indicates that an ionization with an apparent pKa equal to approximately 6.6-6.7 occurs in the reduced form of the enzymes. A heme-linked ionization group in the ferrous form of the enzymes was confirmed by studying the effect of pH on the absorption spectra of isozymes H1 and H4. These spectrophotometric pH titration experiments confirmed the electrochemical results indicating pKa values of 6.59 and 6.69 for reduced isozymes H1 and H4, respectively. These results indicate the presence of a heme-linked ionization of an amino acid in the reduced form of the lignin peroxidase isozymes similar to that of other plant peroxidases.
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PMID:Oxidation-reduction potentials and ionization states of extracellular peroxidases from the lignin-degrading fungus Phanerochaete chrysosporium. 260 98

Compound III (oxyperoxidase) of lignin peroxidase isozyme H8 (pI = 3.5) is formed by either reduction of native ferric enzyme (to ferrous) followed by the reaction with dioxygen or by the addition of excess hydrogen peroxide to resting enzyme. When prepared from the ferrous enzyme, Compound III is stable for days. When formed from excess hydrogen peroxide, the enzyme is rapidly inactivated. However, if the hydrogen peroxide is removed by gel filtration, the resulting Compound III exhibits the same stability as when prepared from ferrous enzyme. Compound III of lignin peroxidase is also relatively unreactive to reducing substrates. Addition of veratryl alcohol to Compound III does not result in any reaction. However, when only 1 equivalent of hydrogen peroxide is added to Compound III in the presence of veratryl alcohol, Compound III is converted to resting enzyme and veratraldehyde formation is detected spectroscopically.
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PMID:On the reactions of lignin peroxidase compound III (isozyme H8). 275 64


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