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)

Laccases are thought to be important to the virulence of many fungal pathogens by producing melanin, a presumed oxygen radical scavenger. A laccase in Cryptococcus neoformans has been shown to synthesize melanin and contributes to the virulence and the survival in macrophages of this fungal pathogen. One C. neoformans laccase gene, LAC1, previously called CNLAC1, has been extensively studied, and we describe a homologous gene, LAC2, that is found 8 kb away from LAC1 in the genome. In this study we report a role for both laccases, in addition to the thiol peroxidase, Tsa1, in oxidative and nitrosative stress resistance mechanisms of C. neoformans. With use of real-time PCR, similar changes in expression of the two laccase genes occur in response to oxidative and nitrosative stresses, but only the regulation of the LAC2 gene during stress is influenced by Tsa1. Both laccases contribute to melanin production using L-dopa as a substrate and are differentially localized in the cell based on green fluorescent protein fusions. A single deletion of either LAC1 or LAC2 alone had no effect on sensitivity to H2O2 or nitric oxide. However, deletion of either LAC1 or LAC2 in combination with a TSA1 deletion resulted in a slight peroxide sensitivity, and a lac2Delta tsa1Delta deletion strain was sensitive to nitric oxide stress. In addition, the deletion of both laccases reduces survival of C. neoformans in primary macrophages. Based on our expression and functional analysis, we propose a novel model for the interaction of these two systems, which are both important for virulence.
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PMID:Distinct stress responses of two functional laccases in Cryptococcus neoformans are revealed in the absence of the thiol-specific antioxidant Tsa1. 1564 75

Lignin peroxidase and laccase gene-specific PCR primers were used to screen 38 diverse basidiomycetes and xylariaceous fungi. Lignin peroxidase gene-specific sequences were obtained for basidiomycetes only and were highly divergent. Possession of laccase genes was relatively widespread among basidiomycetes, and is shown for the first time in Xylariaceae. All sequences were highly conserved with no variation resulting in changes to predicted amino acid sequence. Those basidiomycetes shown to possess lignin peroxidase and laccase genes also produced the enzyme in vitro. Conversely none of the xylariaceous fungi shown to possess laccase genes were able to do so, whilst others decolorized Poly R yet yielded no PCR amplicons.
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PMID:Screening of basidiomycetes and xylariaceous fungi for lignin peroxidase and laccase gene-specific sequences. 1573 69

The degradation of cytokinins in plants is controlled by the flavoprotein cytokinin dehydrogenase (EC 1.5.99.12). Cytokinin dehydrogenase from maize showed the ability to use oxidation products of guaiacol, 4-methylcatechol, acetosyringone and several other compounds as electron acceptors. These results led us to explore the cability for indirect production of suitable electron acceptors by different quinone-generating enzymes. The results reported here revealed that the electron acceptors may be generated in vivo from plant phenolics by other enzymatic systems such as peroxidase and tyrosinase/laccase/catechol oxidase. Histochemical localization of cytokinin dehydrogenase by activity staining and immunochemistry using optical and confocal microscopy showed that cytokinin dehydrogenase is most abundant in the aleurone layer of maize kernels and in phloem cells of the seedling shoots. Cytokinin dehydrogenase was confirmed to be present in the apoplast of cells. Co-staining of enzyme activity for laccase, an enzyme poised to function on the cell wall in the apoplast, in those tissues suggests a possible cooperation of the enzymes in cytokinin degradation. Additionally, the presence of precursors for electron acceptors of cytokinin dehydrogenase was detected in phloem exudates collected from maize seedlings, suggestive of an enzymatic capacity to control cytokinin flux through the vasculature. A putative metabolic connection between cytokinin degradation and conversion of plant phenolics by oxidases was proposed.
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PMID:Tissue localization of cytokinin dehydrogenase in maize: possible involvement of quinone species generated from plant phenolics by other enzymatic systems in the catalytic reaction. 1574 57

The herbicide bentazon (3-isopropyl-1H-2,1,3-benzothiadiazine-4(3H)-one-2,2-dioxide), a relatively inert chemical, and some of its metabolites were incubated with a laccase or a peroxidase in the presence or absence of humic monomers to evaluate the incorporation of the herbicide and its metabolites into humic material by oxidative enzymes. Guaiacol and ferulic acid were used as representative electron donor co-substrates in most of the oxidative coupling reactions. Bentazon and its metabolites, with the exception of hydroxy metabolites, underwent little or no transformation by the two enzymes in the absence of guaiacol and ferulic acid, but in the presence of these co-substrates transformation occurred. The reaction of bentazon with guaiacol in the presence of the laccase or a peroxidase was almost complete in 30 min. 6-Hydroxy- and 8-hydroxy-bentazon were completely transformed by each enzyme both with and without co-substrates. At pH 3.0 and in the presence of laccase and guaiacol, the concentrations of bentazon and its metabolites 2-amino-N-isopropyl-benzamide (AIBA), des-isopropyl-bentazon and 8-chloro-bentazon decreased by 27, 57, 20 and 4%, respectively. The corresponding levels of transformation with peroxidase at pH 3.0 were 9, 70, 30 and 5%, respectively. The extent of transformation decreased with increasing pH. At low pH, the hydroxy-bentazons were completely transformed, followed by (in order of percentage transformation) AIBA, des-isopropyl-bentazon, bentazon and 8-chloro-bentazon. Transformation of bentazon by the laccase increased with increasing guaiacol concentration. In the presence of the peroxidase, the most effective co-substrates for transformation of bentazon were (in decreasing order) catechol, vanillic acid, protocatechuic acid, syringaldehyde and caffeic acid, while in the presence of the laccase, catechol was most effective, followed by caffeic acid, protocatechuic acid and syringaldehyde.
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PMID:Interaction of reactive and inert chemicals in the presence of oxidoreductases: reaction of the herbicide bentazon and its metabolites with humic monomers. 1576 84

During dye decoloration by Trametes versicolor ATCC 20869 in modified Kirk's medium, manganese peroxidase (MnP) and laccase were produced, but not lignin peroxidase, cellobiose dehydrogenase or manganese-independent peroxidase. Purified MnP decolorized azo dyes [amaranth, reactive black 5 (RB5) and Cibacron brilliant yellow] in Mn(2+)-dependent reactions but did not decolorize an anthraquinone dye [Remazol brilliant blue R (RBBR)]. However, the purified laccase decolorized RBBR five to ten times faster than the azo dyes and the addition of a redox mediator, 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid), did not alter decoloration rates. Amaranth and RB5 were decolorized the most rapidly by MnP since they have a hydroxyl group in an ortho position and a sulfonate group in the meta position relative to the azo bond. During a typical batch decoloration with the fungal culture, the ratio of laccase:MnP was 10:1 to 20:1 (based on enzyme activity) and increased to greater than 30:1 after decoloration was complete. Since MnP decolorized amaranth about 30 times more rapidly than laccase per unit of enzyme activity, MnP should have contributed more to decoloration than laccase in batch cultures.
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PMID:Contribution of manganese peroxidase and laccase to dye decoloration by Trametes versicolor. 1583 15

Phanerochaete chrysosporium NRRL 6361 and Pleurotus pulmonarius CBS 664.97 were tested for their ability to grow under nonsterile conditions and to degrade various aromatic hydrocarbons in an aged contaminated soil that also contained high concentrations of heavy metals. After 24 days fungal incubation, carbon-CO2 liberated, an indicator of microbial activity, reached a plateau. At the end of the incubation time (30 days), fungal colonization was clearly visible and was confirmed by ergosterol and cell organic carbon determinations. In spite of unfavorable pH (around 7.4) and the presence of heavy metals, both fungi produced Mn-peroxidase activity. In contrast, laccase and aryl-alcohol oxidase were detected only in the soil treated with P. pulmonarius CBS 664.97 and lignin-peroxidase in that with P. chrysosporium NRRL 6361. No lignin-modifying enzyme activities were present in non-inoculated soil incubated for 30 days (control microcosm). Regardless of the fungus employed, a total removal of naphtalene, tetrachlorobenzene, and dichloroaniline isomers, diphenylether and N-phenyl-1-naphtalenamine, was observed. Significant release of chloride ions was also observed in fungal-treated soil, in comparison with that recorded in the control microcosm. Both fungi led to a significant decrease in soil toxicity, as assessed using two different soil contact assays, including the Lepidium sativum L. germination test and the Collembola mortality test.
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PMID:Degradation of aromatic hydrocarbons by white-rot fungi in a historically contaminated soil. 1585 92

White-rot fungi (WRF) are ubiquitous in nature with their natural ability to compete and survive. WRF are the only organisms known to have the ability to degrade and mineralize recalcitrant plant polymer lignin. Their potential to degrade second most abundant carbon reserve material lignin on the earth make them important link in global carbon cycle. WRF degrade lignin by its unique ligninolytic enzymatic machinery including lignin peroxidase, manganese peroxidase, laccase, cellobiose dehydrogenase, H2O2-generating enzymes, etc. The ligninolytic enzymes system is non-specific, extracellular and free radical based that allows them to degrade structurally diverse range of xenobiotic compounds. Lignin peroxidase and manganese peroxidase carry out direct and indirect oxidation as well as reduction of xenobiotic compounds. Indirect reactions involved redox mediators such as veratryl alcohol and Mn2+. Reduction reactions are carried out by carboxyl, superoxide and semiquinone radicals, etc. Methylation is used as detoxification mechanism by WRF. Highly oxidized chemicals are reduced by transmembrane redox potential. Degradation of a number of environmental pollutants by ligninolytic system of white rot fungi is described in the present review.
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PMID:Degradation of xenobiotic compounds by lignin-degrading white-rot fungi: enzymology and mechanisms involved. 1587 13

Pleurotus ostreatus produces the cellulolytic and hemicellulolytic enzymes endo-1,4-beta-glucanase, exo-1,4-beta-glucanase, 1,4-beta-glucosidase, endo-1,4-beta-xylanase, 1,4-beta-xylosidase, endo-1,4-beta-mannanase and 1,4-beta-mannosidase and ligninolytic enzymes Mn-peroxidase and laccase during growth on wheat straw in the presence and absence of Cu, Mn, Pb, and Zn. This is the first report concerning endo-1,4-beta-mannanase in P. ostreatus. Although the concentrations of trace metals in wheat straw ranged from units to tens of microg g(-1), only 3-6% (Fe, Pb) or 30-45% (Cu, Mn, Zn) of the total amount was extractable and available for the fungus. The substrate colonization rate was only decreased by high concentrations of Cu and Zn; the loss of dry mass differed among treatments in the initial phase of fungal growth, and at the end of the experiment (day 98) it was significantly lower in metal-containing treatments (63-66%) than in the control (70%). The cellulolytic and hemicellulolytic enzyme were prone to a metal effect except for the increase in endo-1,4-beta-glucanase and 1,4-beta-glucosidase in the presence of Zn. Laccase activity was increased by all tested metals, and unlike other white-rot fungi, Mn-peroxidase levels were low in the presence of manganese.
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PMID:Degradation of lignocellulose by Pleurotus ostreatus in the presence of copper, manganese, lead and zinc. 1592 94

Two wood-dwelling ascomycetes, Xylaria hypoxylon and Xylaria polymorpha, were isolated from rotting beech wood. Lignin degradation was studied following the mineralization of a synthetic [formula: see text]-labelled lignin in solid and liquid media. Approximately 9% of the synthetic lignin was mineralized by X. polymorpha during the growth on beech wood meal, and the major fraction (65.5%) was polymerized into water- and dioxan-insoluble material. Both fungi produced laccase (up to 1,200 U l-1) in an agitated complex medium based on tomato juice; peroxidase activity (<80 U l-1) was only detected for X. polymorpha in soybean meal suspension. The enzymatic attack of X. polymorpha on beech wood resulted in the formation of three fractions of water-soluble lignocellulose fragments with molecular masses of 200, 30 (major fraction) and 3 kDa, as demonstrated by high-performance size exclusion chromatography. This fragment pattern differs considerably from that of the white-rot fungus Bjerkandera adusta, which preferentially released smaller lignocellulose fragments (0.8 kDa). The finding that X. polymorpha produced large lignocellulose fragments, along with the fact that high levels of hydrolytic enzymes (esterase 630 U l-1, xylanase 120 U l-1) were detected, indicates the cleavage of bonds between the lignin and hemicellulose moieties.
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PMID:Mineralization of 14C-labelled synthetic lignin and extracellular enzyme activities of the wood-colonizing ascomycetes Xylaria hypoxylon and Xylaria polymorpha. 1602 87

The oxidative cross-coupling of sulfonamide antimicrobials to constituents of natural organic matter was investigated. Sulfonamide antimicrobials were incubated with surrogate humic constituents in the absence and presence of phenoloxidases (viz., peroxidase, laccase, and tyrosinase) or acid birnessite. Substituted phenols were chosen as simple model constituents to determine the structures in humic substances important for cross-coupling reactions. The extent of sulfonamide transformation was evaluated by the disappearance of the parent compound from solution. Incubation with phenoloxidases in the absence of substituted phenols resulted in little or no sulfonamide transformation. In contrast to this, direct oxidation of sulfonamides by acid birnessite was significant. Inclusion of o-diphenols and 2,6-dimethoxyphenols in reaction mixtures resulted in significant phenoloxidase-mediated transformation of sulfonamides and enhanced antimicrobial transformation in the presence of acid birnessite. Phenolic compounds with other substitution patterns were less effective in promoting sulfonamide transformation. Nuclear magnetic resonance spectroscopy experiments provided direct evidence of peroxidase-mediated covalent cross-coupling of sulfamethazine with syringic and protocatechuic acids. Our results indicate that sulfonamide antimicrobials may be chemically incorporated into humic substances. This may result in their diminished mobility, bioavailability, and biological activity.
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PMID:Cross-coupling of sulfonamide antimicrobial agents with model humic constituents. 1604 82


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