Evidence for Veratryl Alcohol as a Redox Mediator in Lignin Peroxidase-Catalyzed Oxidation

Goodwin, Douglas C.; Aust, Steven D.; Grover, Thomas A.

doi:10.1021/bi00015a017

Cited by 84 publications

(68 citation statements)

References 20 publications

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“…Kinetic simulation of mediation reveals two unique aspects which are born out by the data: (i) veratryl alcohol oxidation does not occur until the secondary substrate is depleted (lag phase kinetic traces) and (ii) the effect of veratryl alcohol on the oxidation of the secondary substrate exhibits saturation kinetics. Both of these properties are observed with chloropromazine (25) and guaiacol (26). These properties differ from those observed with anisyl alcohol where no lag phases are observed and an optimal rate is observed at low veratryl alcohol concentrations.…”

Section: Discussionmentioning

confidence: 65%

“…This role was initially formulated from data showing the ability of veratryl alcohol to enhance the oxidation of recalcitrant compounds that are not directly oxidized by the enzyme. Lignin (24), anisyl alcohol (10), 4-MMA (10), chloropromazine (25), and guaiacol (26) are only oxidized by LP if veratryl alcohol is included in the reaction mixture. Although the mediation mechanism provided a suitable explanation for the phenomenon and provided a model for how a large bulky enzyme could degrade an insoluble large bulky polymer, there were chemical arguments against the model.…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Oxidation of 4-Methoxymandelic Acid by Lignin Peroxidase

Tien

1997

Journal of Biological Chemistry

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The mechanism of veratryl alcohol-mediated oxidation of 4-methoxymandelic acid by lignin peroxidase was studied by kinetic methods. For monomethoxylated substrates not directly oxidized by lignin peroxidase, veratryl alcohol has been proposed to act as a redox mediator. Our previous study showed that stimulation of anisyl alcohol oxidation by veratryl alcohol was not due to mediation but rather due to the requirement of veratryl alcohol to complete the catalytic cycle. Anisyl alcohol can react with compound I but not with compound II. In contrast, veratryl alcohol readily reduces compound II. We demonstrate in the present report that the oxidation of 4-methoxy mandelic acid is mediated by veratryl alcohol. Increasing veratryl alcohol concentration in the presence of 2 mM 4-methoxymandelic acid resulted in increased oxidation of 4-methoxymandelic acid yielding anisaldehyde. This is in contrast to results obtained with anisyl alcohol where increased concentrations of veratryl alcohol caused a decrease in product formation. ESR spectroscopy demonstrated that 4-methoxymandelic acid caused a decrease in the enzymebound veratryl alcohol cation radical signal, which is consistent with its reaction at the active site of the enzyme.To degrade the aromatic polymer lignin, the white-rot fungus Phanerochaete chrysosporium secretes H 2 O 2 (1), and two families of H 2 O 2 -utilizing enzymes, the lignin peroxidase (LP) 1 and manganese peroxidases (MnP). The MnPs catalyze the oxidation of Mn 2ϩ to Mn 3ϩ (2) whereas the LPs catalyze the oxidation of phenolic and nonphenolic methoxylated aromatic substrates (3). The catalytic cycle of both peroxidases is similar to that of other peroxidases. The enzyme is first oxidized by H 2 O 2 to form a two-electron-oxidized intermediate, compound I (4). Compound I then returns to the resting ferric enzyme by two sequential one-electron reduction steps producing two, oneelectron-oxidized products. The one-electron oxidized species of the enzyme formed during turnover is referred to as compound II. Unique to these fungal peroxidases is the recalcitrant nature of their substrate (5). Both act on substrates that other peroxidases are not capable of oxidizing.The role and mechanism by which the LP and MnP interact with lignin is yet to be elucidated. For both enzymes, the role of mediators has been proposed. With MnP, the mediation phenomenon is well characterized and widely accepted. Complexed Mn 2ϩ (6, 7) is oxidized by MnP and diffuses away from the active site of the enzyme to oxidize lignin (8). In the case of LP, the role of mediators and the mechanism by which lignin is depolymerized by LP is still unknown. A key component of LP catalysis is veratryl alcohol, a secondary metabolite also produced by ligninolytic cultures of P. chrysosporium (9). Harvey et al. (10) proposed that veratryl alcohol is the mediator for LP as Mn 2ϩ is the mediator for MnP. They proposed that the initial one-electron oxidation of veratryl alcohol forms the cation radical which then diffuses away from the active s...

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Section: Discussionmentioning

confidence: 65%

Section: Discussionmentioning

confidence: 99%

Oxidation of 4-Methoxymandelic Acid by Lignin Peroxidase

Tien

1997

Journal of Biological Chemistry

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“…The higher OP of veratryl alcohol at pH 3.5 (1.36 V versus normal hydrogen electrode) (49) in comparison to phenolic substrates (0.79 -1.17 V versus normal hydrogen electrode, Table III) is probably the driving force for veratryl alcohol-mediated oxidation of phenolic substrates, which has been extensively documented (4,6,17,48,50,51). The radical cation formed upon oxidation of veratryl alcohol is preferentially reduced by phenolic substrate.…”

Section: Mechanistic Features Of Oxidation Of Phenolic Substrates-mentioning

confidence: 84%

Mechanistic Features of Lignin Peroxidase-catalyzed Oxidation of Substituted Phenols and 1,2-Dimethoxyarenes

Ward

Hadar

Bilkis

et al. 2003

Journal of Biological Chemistry

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The steady state kinetic parameters K m and k cat for the oxidation of phenolic substrates by lignin peroxidase correlated with the presteady state kinetic parameters K d and k for the reaction of the enzyme intermediate compound II with the substrates, indicating that the latter is the rate-limiting step in the catalytic cycle. ln K m and ln K d values for phenolic substrates correlated with redox properties, unlike ln k cat and ln k. This finding suggests that in contrast to horseradish peroxidase, electron transfer is not the rate-limiting step during oxidation by lignin peroxidase compound II. A mechanism is proposed for lignin peroxidase compound II reactions consisting of an equilibrium electron transfer step followed by a subsequent rate-limiting step. Analysis of the correlation coefficients for linear relationships between ln K d and ln K m and different calculated redox parameters supports a mechanism in which the acidic forms of phenols are oxidized by lignin peroxidase and electron transfer is coupled with proton transfer. 1,2-Dimethoxyarenes did not comply with the trend for phenolic substrates, which may be a result of more than one substrate binding site on lignin peroxidase and/or alternative binding modes. This behavior was supported by analogue studies with the 1,2-dimethoxyarenes veratric acid and veratryl aldehyde, both of which are not oxidized by lignin peroxidase. Inclusion of either had little effect on the rate of oxidation of phenolic substrates yet resulted in a decrease in the oxidation rate of 1,2-dimethoxyarene substrates, which was considerable for veratryl alcohol and less pronounced for 3,4-dimethoxyphenethylalcohol and 3,4-dimethoxycinnamic acid, in particular in the presence of veratric acid. Lignin peroxidases (LIP)1 play a central role in the biodegradation of the plant cell wall constituent lignin by white-rot fungi, the most extensively studied of which is Phanerochaete chrysosporium (1, 2). LIP possesses a higher redox potential and lower pH value than any other peroxidase and, in accordance, exhibits broader substrate specificity (3). Like other peroxidases, it is capable of oxidizing phenolic compounds (4 -6) as well as ring-and N-substituted anilines (7-9). However, it is unique in its ability to oxidize certain non-phenolic aromatic substrates possessing high redox potential values, such as substituted aromatic ethers (e.g. veratryl alcohol) (10 -13) and thioethers (14).The catalytic cycle of LIP is similar to that of other peroxidases (15, 16). The reaction of native ferric enzyme (Fe-LIP; Fe 3ϩ PR (porphyrin)) with H 2 O 2 yields LIP-compound I (LIPI), a complex of high valence oxo-iron and PR radical cation (Fe 4ϩ ϭ O PR . ϩ ). One-electron oxidation of a reducing substrate by LIPI yields a radical cation and the one electron-oxidized enzyme intermediate, LIP-compound II (LIPII: Fe 4ϩ ϭ O PR). A single one-electron oxidation of a second substrate molecule by LIPII results in the formation of another radical cation and the release of a molecule of water, with the enz...

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“…One suggestion considers VA .+ as a redox mediator in the oxidation of lignin [89]. VA .+ is capable of mediating oxidation of secondary substrates typically not oxidized by LiP [69,89,[96][97][98]. The radical cation has also been implicated in the protection of LiP from inactivation because of the formation of LiP-III by prolonged incubation with or in excess of H 2 O 2 .…”

Section: Oxidation Of Veratryl Alcoholmentioning

confidence: 99%

Structure and Action Mechanism of Ligninolytic Enzymes

Wong

2008

Appl Biochem Biotechnol

724

471

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Lignin is the most abundant renewable source of aromatic polymer in nature, and its decomposition is indispensable for carbon recycling. It is chemically recalcitrant to breakdown by most organisms because of the complex, heterogeneous structure. The white-rot fungi produce an array of extracellular oxidative enzymes that synergistically and efficiently degrade lignin. The major groups of ligninolytic enzymes include lignin peroxidases, manganese peroxidases, versatile peroxidases, and laccases. The peroxidases are heme-containing enzymes with catalytic cycles that involve the activation by H2O2 and substrate reduction of compound I and compound II intermediates. Lignin peroxidases have the unique ability to catalyze oxidative cleavage of C-C bonds and ether (C-O-C) bonds in non-phenolic aromatic substrates of high redox potential. Manganese peroxidases oxidize Mn(II) to Mn(III), which facilitates the degradation of phenolic compounds or, in turn, oxidizes a second mediator for the breakdown of non-phenolic compounds. Versatile peroxidases are hybrids of lignin peroxidase and manganese peroxidase with a bifunctional characteristic. Laccases are multi-copper-containing proteins that catalyze the oxidation of phenolic substrates with concomitant reduction of molecular oxygen to water. This review covers the chemical nature of lignin substrates and focuses on the biochemical properties, molecular structures, reaction mechanisms, and related structures/functions of these enzymes.

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Evidence for Veratryl Alcohol as a Redox Mediator in Lignin Peroxidase-Catalyzed Oxidation

Cited by 84 publications

References 20 publications

Oxidation of 4-Methoxymandelic Acid by Lignin Peroxidase

Oxidation of 4-Methoxymandelic Acid by Lignin Peroxidase

Mechanistic Features of Lignin Peroxidase-catalyzed Oxidation of Substituted Phenols and 1,2-Dimethoxyarenes

Structure and Action Mechanism of Ligninolytic Enzymes

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