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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)

Stability of laccase isoenzymes from a crude extract obtained from Fomes sclerodermeus grown on wheat bran medium was studied. The variables assessed were temperature, pH and additives. As revealed by PAGE, three bands of laccase, each with different thermal inactivation pattern, were detected in the crude extract: after 6h at 50 degrees C and pH 8, Lc2 was the most resistant, while the Lc1 and Lc3 bands were almost completely inactivated. This pattern of inactivation was observed at all temperatures and pH tested. Laccase activity was more stable in the 5-10 pH range when incubated at 40 and 50 degrees C; at 30 degrees C and 24h the enzyme remained fully active in the 3-11 pH range. The effect of additives (veratryl alcohol, trehalose, glycerol, mannitol, glutaraldehyde, CuSO(4) and 1-HBT) on laccase stability was tested. The stability was enhanced with CuSO(4) (1.25 mM), glycerol (0.2%) and mannitol (1%). The presence of both CuSO(4) and glycerol caused a 3-fold increase in the half-life values.
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PMID:Stabilization studies of Fomes sclerodermeus laccases. 1732 Mar 85

A new laccase gene (lacC) was cloned from the genomic DNA isolated from Trametes sp. 420, a new laccase-producing fungus, using the degenerate primers based on the conserved copper-binding regions in fungal laccases. Long distance-inverse PCR (LD-IPCR) was used to amplify the flanking sequences of the gene. The lacC DNA sequence obtained was 3640 base pairs (bp), including the entire open reading frame (2263bp) and the 5'-and 3'-noncoding regions. The lacC cDNA sequence is 1560bp, encoding a 519 amino acid protein. The deduced peptide sequence of LacC contains ten putative N-glycosylation sites and four conserved copper-binding regions. The lacC cDNA without its signal sequence was cloned into the expression vector pPIC9K through the pPIC9 plasmid and transformed into the Pichia pastoris strain GS115.The positive transformant was cultured at 20 degrees C in BMM medium containing 0.3mmol/L CuSO4 and 0.8% alanine, with the yield of the recombinant laccase rLacC being 1.62 x 10(4) U/L after a 9-day cell growth. Furthermore, the crude enzyme was used to decolorize several synthetic dyes at a final concentration of 50mg/L. The results showed that rLacC (6U/L) possessed the valuable ability to decolorize dyes of triarylmethane and azo types tested. The presence of low molecular weight redox mediators of ABTS and HBT increased the efficiency and velocity of dye decolorization significantly.
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PMID:[Cloning and heterologous expression of the gene of laccase C from Trametes sp. 420 and potential of recombinant laccase in dye decolorization]. 1743 24

Dyes belonging to the mono-, di-, tri- and poly-azo as well as anthraquinonic and mono-azo Cr-complexed classes, chosen among the most utilized in textile applications, were employed for a comparative enzymatic decolorization study using the extracellular crude culture extracts from the white rot fungus Funalia (Trametes) trogii grown on different culture media and activators able to trigger different levels of expression of oxidizing enzymes: laccase and cellobiose dehydrogenase. Laccase containing extracts were capable to decolorize some dyes from all the different classes analyzed, whereas the recalcitrant dyes were subjected to the combined action of laccase and the chemical mediator HBT, or laccase plus cellobiose dehydrogenase. Correlations among the decolorization degree of the various dyes and their electronic and structural diversities were rationalized and discussed. The utilization of cellobiose dehydrogenase in support to the activity of laccase for the decolorization of azo textile dyes resulted in substantial increases in decolorization for all the refractory dyes proving to be a valid alternative to more expensive and less environmentally friendly chemical treatments of textile dyes wastes.
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PMID:Fungal laccase, cellobiose dehydrogenase, and chemical mediators: combined actions for the decolorization of different classes of textile dyes. 1828 Dec 11

Different operating conditions (viz. pulp consistency, oxygen pressure and treatment time) in the biobleaching of eucalyptus kraft pulp with the laccase-HBT system was tested in order to describe their effect and normalize a biobleaching protocol. A high O(2) pressure (0.6MPa) was found to result in improved laccase-assisted delignification of the pulp. Also, a high pulp consistency (10%) and a short treatment time (2h) proved the best choices with a view to obtaining good pulp properties (kappa number and ISO brightness) under essentially mild conditions. The laccase-HBT treatment was found to result in slight delignification (in the form of a 20-27% decrease in kappa number); however, an alkaline extraction stage raised delignification to 41-45%, a much higher level than those obtained in the control tests (16-23%). Also, the use of hydrogen peroxide in the extraction stage resulted in improved brightness (14-19%), but in scarcely improved delignification (4-7%). Treating the pulp with the laccase-HBT system reduced the amount of hydrogen peroxide required for subsequent alkaline bleaching by a factor of 3-4 relative to control tests.
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PMID:Laccase-HBT bleaching of eucalyptus kraft pulp: influence of the operating conditions. 1849 77

Three new chromatographic forms of Dichomitus squalens manganese-dependent peroxidase (MnP) were isolated from wheat-straw cultures using Mono Q and connective interaction media (CIM) fast protein liquid chromatography. Enzymes revealed identical molar mass of 50 kDa (estimated by SDS-PAGE) and pI values of 3.5, however, they varied in Km values obtained for Mn2+ oxidation. The addition of wood and straw methanol extracts to the cultures showed that the production of MnPs in wheat-straw cultures was influenced rather by the type of cultivation than by phenolic compounds from lignocellulosic material which induced laccase production. The purified CIM1 MnP was able to decolorize selected azo and anthraquinone dyes more rapidly than laccase Lc1. In vitro dye decolorization showed a synergistic cooperation of MnP and laccase. In the case of CSB degradation MnP prevented from the production of a differently colored substance that could be produced after CSB degradation by laccase-HBT system.
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PMID:Implication of Dichomitus squalens manganese-dependent peroxidase in dye decolorization and cooperation of the enzyme with laccase. 1938 71

Mixtures of equal amounts of the erythro and threo forms of the phenolic arylglycerol beta-aryl ether 1-(4-hydroxy-3-methoxyphenyl)-2-(2-methoxyphenoxy)-1,3-propanediol were oxidized (i) with laccases from Trametes versicolor, Agaricus bisporus, Myceliophthora thermophila and Rhus vernicifera, (ii) with laccase-mediator systems consisting of T. versicolor laccase and ABTS or HBT, and (iii) with various model oxidants including cerium(IV) ammonium nitrate (CAN), lignin peroxidase, Fenton's reagent, and lead(IV) tetraacetate (LTA). All the laccases exhibited a similar preferential degradation of the threo form. The mediator ABTS counteracted the threo preference of laccase, but the mediator HBT did not affect it. The outer-sphere model oxidants CAN and lignin peroxidase showed a preferential degradation of the threo form. LTA and Fenton's reagent did not exhibit any stereo-preference. The results suggest that laccases of different origin, primary structure, and redox potential behave as typical outer-sphere oxidants in their interaction with the diastereomers of the arylglycerol beta-aryl ether.
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PMID:Oxidation of the erythro and threo forms of the phenolic lignin model compound 1-(4-hydroxy-3-methoxyphenyl)-2-(2-methoxyphenoxy)-1,3-propanediol by laccases and model oxidants. 1964 32

High-quality flax pulp was bleached in a short totally-chlorine-free (TCF) sequence. The LP biobleaching sequence includes an enzyme treatment with laccase in the presence of HBT as mediator (L stage) and a hydrogen peroxide stage (P stage). The operating conditions for the laccase HBT system were optimized by using a sequential statistical plan involving four variables, the influence of which on the properties of the pulp after the P stage was examined over enclosed operation conditions regarding a future industrial application. Mathematical models accurately predicting both pulp properties in terms of the previous four variables. This biobleaching sequence allows obtaining an increase in ISO brightness of 40% and a delignification of 80%. Process variables optimization in flax pulp biobleaching allows establishing the application conditions most appropriated to obtain certain pulp properties and that turn out to be easily adaptable to existing industrial processes. As a novelty, toxicity measurements were determined in L stage effluents. The results of toxicity show that it is possible to apply this LP sequence without having a negative environmental impact.
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PMID:Optimization of laccase-mediator system in producing biobleached flax pulp. 1969 85

Laccase, an enzyme responsible for aerobic transformations of natural phenolics, in industrial applications requires the presence of low-molecular substances known as mediators, which accelerate oxidation processes. However, the use of mediators is limited by their toxicity and the high costs of exploitation. The activation of extracellular laccase in growing fungal culture with highly diluted mediators, ABTS and HBT is described. Two high laccase-producing fungal strains, Trametes versicolor and Cerrena unicolor, were used in this study as a source of enzyme. Selected dilutions of the mediators significantly increased the activity of extracellular laccase during 14 days of cultivation what was distinctly visible in PAGE technique and in colorimetric tests. The same mediator dilutions increased demethylation properties of laccase, which was demonstrated during incubation of enzyme with veratric acid. It was established that the activation effect was assigned to specific dilutions of mediators. Our dose-response dilution process smoothly passes into the range of action of homeopathic dilutions and is of interest for homeopaths.
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PMID:Influence of very low doses of mediators on fungal laccase activity - nonlinearity beyond imagination. 1973 25

The aim of this work was to obtain a LMS pre-treatment applicable to industrial TCF bleaching. Kraft pulp from Eucalyptus globulus was treated at 40 degrees C/pH 3 and 60 degrees C/pH 5 for 1h using an extracellular fluid enriched in laccase produced by Pycnoporus sanguineus and acetosyringone as mediator (HBT was used as a control mediator) (L). Alkaline extraction (E) and hydrogen peroxide (P) stages were then assayed. The LEP alternative was an efficient sequence to bleach kraft pulp since the enzymatic pre-treatment boosted the subsequent chemical bleaching. The best L pre-treatment was obtained with laccase-acetosyringone at 40 degrees C/pH 3. It reduces kappa number and hexenuronic acids, increases pulp viscosity, lowers hydrogen peroxide consumption down to an 87.4% (94.0% without L) and enhances brightness up to a 59% ISO (51% ISO without L).
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PMID:Kraft pulp biobleaching using an extracellular enzymatic fluid produced by Pycnoporus sanguineus. 1985 61

Using an enzyme-based stage involving a xylanase (X) or laccase (as part of a laccase-mediator system, L) in a bleaching process can help reduce reagent consumption and hence its environmental impact. In this work, both types of enzymes were applied to eucalypt pulp. The influence of process variables in the laccase-mediator treatment (viz. laccase dose, HBT dose and reaction time) was assessed by using a three-variable sequential statistical plan. The effect of a pretreatment with X on the previous variables was also assessed. Kappa number and brightness models for the L stage and XL sequence were found to perform disparately, which suggests the formation of lignin derivatives interfering with brightness measurements. The L system oxidized readily accessible lignin within the first hours of treatment and affected the contents in cellulose and hexenuronic acids (HexA) of the resulting pulp. Xylanase facilitated access of the laccase-HBT system to lignin and HexA in cellulose fibres. The L treatment increased effluent properties such as Microtox toxicity, COD and colour, and led to strong inactivation of the enzyme. The increased toxicity of the effluents was due to HBT; based on statistical data, however, the effect can be reduced by lowering the mediator dose.
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PMID:Boosting the effect of a laccase-mediator system by using a xylanase stage in pulp bleaching. 2011 67


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