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:1.10.3.2 (laccase)
4,656 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Laccase is a copper-containing phenoloxidase, involved in lignin degradation by white rot fungi. The laccase substrate range can be extended to include nonphenolic lignin subunits in the presence of a noncatalytic cooxidant such as 2, 2'-azinobis(3-ethylbenzthiazoline-6-sulfonate) (ABTS), with ABTS being oxidized to the stable cation radical, ABTS.+, which accumulates. In this report, we demonstrate that the ABTS.+ can be efficiently reduced back to ABTS by physiologically occurring organic acids such as oxalate, glyoxylate, and malonate. The reduction of the radical by oxalate results in the formation of H2O2, indicating the formation of O2.- as an intermediate. O2.- itself was shown to act as an ABTS.+ reductant. ABTS.+ reduction and H2O2 formation are strongly stimulated by the presence of Mn2+, with accumulation of Mn3+ being observed. Additionally, 4-methyl-O-isoeugenol, an unsaturated lignin monomer model, is capable of directly reducing ABTS.+. These data suggest several mechanisms for the reduction of ABTS.+ which would permit the effective use of ABTS as a laccase cooxidant at catalytic concentrations.
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PMID:Reduction of the 2,2'-Azinobis(3-ethylbenzthiazoline-6-sulfonate) cation radical by physiological organic acids in the absence and presence of manganese 960 10

The basidiomycetous fungus Nematoloma frowardii produced manganese peroxidase (MnP) as the predominant ligninolytic enzyme during solid-state fermentation (SSF) of wheat straw. The purified enzyme had a molecular mass of 50 kDa and an isoelectric point of 3.2. In addition to MnP, low levels of laccase and lignin peroxidase were detected. Synthetic 14C-ring-labelled lignin (14C-DHP) was efficiently degraded during SSF. Approximately 75% of the initial radioactivity was released as 14CO2, while only 6% was associated with the residual straw material, including the well-developed fungal biomass. On the basis of this finding we concluded that at least partial extracellular mineralization of lignin may have occurred. This conclusion was supported by the fact that we detected high levels of organic acids in the fermented straw (the maximum concentrations in the water phases of the straw cultures were 45 mM malate, 3.5 mM fumarate, and 10 mM oxalate), which rendered MnP effective and therefore made partial direct mineralization of lignin possible. Experiments performed in a cell-free system, which simulated the conditions in the straw cultures, revealed that MnP in fact converted part of the 14C-DHP to 14CO2 (which accounted for up to 8% of the initial radioactivity added) and 14C-labelled water-soluble products (which accounted for 43% of the initial radioactivity) in the presence of natural levels of organic acids (30 mM malate, 5 mM fumarate).
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PMID:Production of manganese peroxidase and organic acids and mineralization of 14C-labelled lignin (14C-DHP) during solid-state fermentation of wheat straw with the white rot fungus nematoloma frowardii 1022 71

A purified and electrophoretically homogeneous blue laccase from the litter-decaying basidiomycete Stropharia rugosoannulata with a molecular mass of approximately 66 kDa oxidized Mn(2+) to Mn(3+), as assessed in the presence of the Mn chelators oxalate, malonate, and pyrophosphate. At rate-saturating concentrations (100 mM) of these chelators and at pH 5.0, Mn(3+) complexes were produced at 0.15, 0.05, and 0.10 micromol/min/mg of protein, respectively. Concomitantly, application of oxalate and malonate, but not pyrophosphate, led to H(2)O(2) formation and tetranitromethane (TNM) reduction indicative for the presence of superoxide anion radical. Employing oxalate, H(2)O(2) production, and TNM reduction significantly exceeded those found for malonate. Evidence is provided that, in the presence of oxalate or malonate, laccase reactions involve enzyme-catalyzed Mn(2+) oxidation and abiotic decomposition of these organic chelators by the resulting Mn(3+), which leads to formation of superoxide and its subsequent reduction to H(2)O(2). A partially purified manganese peroxidase (MnP) from the same organism did not produce Mn(3+) complexes in assays containing 1 mM Mn(2+) and 100 mM oxalate or malonate, but omitting an additional H(2)O(2) source. However, addition of laccase initiated MnP reactions. The results are in support of a physiological role of laccase-catalyzed Mn(2+) oxidation in providing H(2)O(2) for extracellular oxidation reactions and demonstrate a novel type of laccase-MnP cooperation relevant to biodegradation of lignin and xenobiotics.
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PMID:Laccase-catalyzed oxidation of Mn(2+) in the presence of natural Mn(3+) chelators as a novel source of extracellular H(2)O(2) production and its impact on manganese peroxidase. 1208 36

The white rot basidiomycete Trametes (Coriolus) versicolor can substantially increase the brightness and decrease the lignin content of washed, unbleached hardwood kraft pulp (HWKP). Monokaryotic strain 52J was used to study how HWKP and the lignin in HWKP affect the carbon metabolism and secretions of T. versicolor. Earlier work indicated that a biobleaching culture supernatant contained all components necessary for HWKP biobleaching and delignification, but the supernatant needed frequent contact with the fungus to maintain these activities. Thus, labile small fungal metabolites may be the vital biobleaching system components renewed or replaced by the fungus. Nearly all of the CO(2) evolved by HWKP-containing cultures came from the added glucose, indicating that HWKP is not an important source of carbon or energy during biobleaching. Carbon dioxide appeared somewhat earlier in the absence of HWKP, but the culture partial O(2) pressure was little affected by the presence of pulp. The presence of HWKP in a culture markedly increased the culture's production of a number of acidic metabolites, including 2-phenyllactate, oxalate, adipate, glyoxylate, fumarate, mandelate, and glycolate. Although the total concentration of these pulp-induced metabolites was only 4.3 mM, these compounds functioned as effective manganese-complexing agents for the manganese peroxidase-mediated oxidation of phenol red, propelling the reaction at 2.4 times the rate of 50 mM sodium malonate, the standard chelator-buffer. The presence of HWKP in a culture also markedly stimulated fungal secretion of the enzymes manganese peroxidase, cellulase, and cellobiose-quinone oxidoreductase, but not laccase (phenol oxidase) or lignin peroxidase.
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PMID:Effects of Kraft Pulp and Lignin on Trametes versicolor Carbon Metabolism. 1634 63

The ligninolytic system of the basidiomycete Ceriporiopsis subvermispora is composed of manganese peroxidase (MnP) and laccase. In this work, the source of extracellular hydrogen peroxide required for MnP activity was investigated. Our attention was focused on the possibility that hydrogen peroxide might be generated by MnP itself through the oxidation of organic acids secreted by the fungus. Both oxalate and glyoxylate were found in the extracellular fluid of C. subvermispora cultures grown in chemically defined media, where MnP is also secreted. The in vivo oxidation of oxalate was measured; CO(2) evolution was monitored after addition of exogenous [C]oxalate to cultures at constant specific activity. In standard cultures, evolution of CO(2) from oxalate was maximal at day 6, although the MnP titers were highest at day 12, the oxalate concentration was maximal (2.5 mM) at day 10, and the glyoxylate concentration was maximal (0.24 mM) at day 5. However, in cultures containing low nitrogen levels, in which the pH is more stable, a better correlation between MnP titers and mineralization of oxalate was observed. Both MnP activity and oxidation of [C]oxalate were negligible in cultures lacking Mn(II). In vitro assays confirmed that Mn(II)-dependent oxidation of [C]oxalate by MnP occurs and that this reaction is stimulated by glyoxylate at the concentrations found in cultures. In addition, both organic acids supported phenol red oxidation by MnP without added hydrogen peroxide, and glyoxylate was more reactive than oxalate in this reaction. Based on these results, a model is proposed for the extracellular production of hydrogen peroxide by C. subvermispora.
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PMID:Manganese Peroxidase-Dependent Oxidation of Glyoxylic and Oxalic Acids Synthesized by Ceriporiopsis subvermispora Produces Extracellular Hydrogen Peroxide. 1634 95

The effect of cadmium (Cd) on fungal growth, Cd bioaccumulation and biosorption, and on the formation of potential heavy metal response indicators such as thiols, oxalate, and laccase was investigated in the white rot fungi Cerrena unicolor andAbortiporus biennis. Only the highest Cd concentration employed (200 microM) inhibited growth of C. unicolor, whereas already lower Cd concentrations caused decreasing mycelia dry weights in A. biennis. Cd biosorption onto the mycelial surface was the predominant Cd sequestration mechanism in C. unicolor. Surface-bound and bioaccumulated Cd concentrations were essentially in the same range in A. biennis, leading to considerably higher intracellular Cd concentrations in A. biennis than in C. unicolor. Oxalate and laccase were produced by both of the fungal strains and their extracellular levels were elevated upon Cd exposure. Oxalate concentrations and laccase titres were considerably higher in C. unicolor than in A. biennis. Both fungi responded to increasing Cd concentrations by increasing intracellular amounts of thiol compounds (cysteine, gamma-glutamylcysteine, glutathione in both its reduced and oxidized form) but Cd application increased the amounts of thiols to a higher extend in A. biennis. Taken together, these species-specific responses towards Cd suggest that C. unicolor possesses a more efficient system than A. biennis to keep intracellular Cd concentrations low.
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PMID:Species-specific Cd-stress response in the white rot basidiomycetes Abortiporus biennis and Cerrena unicolor. 1650 30

The principal possibility of enzymatic oxidation of manganese ions by fungal Trametes hirsuta laccase in the presence of oxalate and tartrate ions, whereas not for plant Rhus vernicifera laccase, was demonstrated. Detailed kinetic studies of the oxidation of different enzyme substrates along with oxygen reduction by the enzymes show that in air-saturated solutions the rate of oxygen reduction by the T2/T3 cluster of laccases is fast enough not to be a readily noticeable contribution to the overall turnover rate. Indeed, the limiting step of the oxidation of high-redox potential compounds, such as chelated manganese ions, is the electron transfer from the electron donor to the T1 site of the fungal laccase.
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PMID:Enzymatic oxidation of manganese ions catalysed by laccase. 1897 93

The induction of hydroxyl radical (OH) production via quinone redox cycling in white-rot fungi was investigated to improve pollutant degradation. In particular, we examined the influence of 4-methoxybenzaldehyde (anisaldehyde), Mn(2+), and oxalate on Pleurotus eryngii OH generation. Our standard quinone redox cycling conditions combined mycelium from laccase-producing cultures with 2,6-dimethoxy-1,4-benzoquinone (DBQ) and Fe(3+)-EDTA. The main reactions involved in OH production under these conditions have been shown to be (i) DBQ reduction to hydroquinone (DBQH(2)) by cell-bound dehydrogenase activities; (ii) DBQH(2) oxidation to semiquinone (DBQ(-)) by laccase; (iii) DBQ(-) autoxidation, catalyzed by Fe(3+)-EDTA, producing superoxide (O(2)(-)) and Fe(2+)-EDTA; (iv) O(2)(-) dismutation, generating H(2)O(2); and (v) the Fenton reaction. Compared to standard quinone redox cycling conditions, OH production was increased 1.2- and 3.0-fold by the presence of anisaldehyde and Mn(2+), respectively, and 3.1-fold by substituting Fe(3+)-EDTA with Fe(3+)-oxalate. A 6.3-fold increase was obtained by combining Mn(2+) and Fe(3+)-oxalate. These increases were due to enhanced production of H(2)O(2) via anisaldehyde redox cycling and O(2)(-) reduction by Mn(2+). They were also caused by the acceleration of the DBQ redox cycle as a consequence of DBQH(2) oxidation by both Fe(3+)-oxalate and the Mn(3+) generated during O(2)(-) reduction. Finally, induction of OH production through quinone redox cycling enabled P. eryngii to oxidize phenol and the dye reactive black 5, obtaining a high correlation between the rates of OH production and pollutant oxidation.
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PMID:Enhancing the production of hydroxyl radicals by Pleurotus eryngii via quinone redox cycling for pollutant removal. 1937 90

Brown rot basidiomycetes initiate wood decay by producing extracellular reactive oxygen species that depolymerize the structural polysaccharides of lignocellulose. Secreted fungal hydroquinones are considered one contributor because they have been shown to reduce Fe(3+), thus generating perhydroxyl radicals and Fe(2+), which subsequently react further to produce biodegradative hydroxyl radicals. However, many brown rot fungi also secrete high levels of oxalate, which chelates Fe(3+) tightly, making it unreactive with hydroquinones. For hydroquinone-driven hydroxyl radical production to contribute in this environment, an alternative mechanism to oxidize hydroquinones is required. We show here that aspen wood undergoing decay by the oxalate producer Postia placenta contained both 2,5-dimethoxyhydroquinone and laccase activity. Mass spectrometric analysis of proteins extracted from the wood identified a putative laccase (Joint Genome Institute P. placenta protein identification number 111314), and heterologous expression of the corresponding gene confirmed this assignment. Ultrafiltration experiments with liquid pressed from the biodegrading wood showed that a high-molecular-weight component was required for it to oxidize 2,5-dimethoxyhydroquinone rapidly and that this component was replaceable by P. placenta laccase. The purified laccase oxidized 2,5-dimethoxyhydroquinone with a second-order rate constant near 10(4) M(-1) s(-1), and measurements of the H(2)O(2) produced indicated that approximately one perhydroxyl radical was generated per hydroquinone supplied. Using these values and a previously developed computer model, we estimate that the quantity of reactive oxygen species produced by P. placenta laccase in wood is large enough that it likely contributes to incipient decay.
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PMID:Laccase and its role in production of extracellular reactive oxygen species during wood decay by the brown rot basidiomycete Postia placenta. 2015 18

Studies were carried on the decolorization of the textile dye reactive blue 220 (RB220) by a novel isolate of Lentinus crinitus fungi. The optimal conditions for the production of destaining activity were obtained in media containing intermediate concentrations of ammonium oxalate and glucose (10 g L(-1)) as nitrogen and carbon sources, respectively, at 28 degrees C and pH 5.5. Maximum decolorization efficiency against RB220 achieved in this study was around 95%. Ultra-violet and visible (UV-vis) spectrophotometric analyses, before and after decolorization, suggest that decolorization was due to biodegradation. This effect was associated with a putative low molecular weight laccase (41 kDa) displaying good tolerance to a wide range of pH values, salt concentrations and temperatures, suggesting a potential role for this organism in the remediation of real dye containing effluents.
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PMID:Decolorization and biodegradation of reactive blue 220 textile dye by Lentinus crinitus extracellular extract. 2045 21


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