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)

The effects of laccase-natural mediator systems (LMS) on sisal pulp and their potential for either biobleaching or functionalizing (via radical-coupling) its fibres were investigated. The enzyme treatment (L stage) was followed by extraction with hydrogen peroxide in order to determine whether observable effects could be enhanced by removing LMS-modified lignin. Four different plant phenols [viz. the p-hydroxycinnamic compounds sinapic acid (SNC), ferulic acid (FRC), coniferyl aldehyde (CLD) and sinapyl aldehyde (SLD)] were used as laccase redox mediators and their effects on pulp and effluents compared with those of the synthetic compound 1-hydroxybenzotriazole (HBT). During the L stage performed with HBT, laccase underwent a loss of 99% and 78% of the initial activity, in the absence and presence of pulp, respectively. With natural mediators inactivation was markedly reduced, being the residual activity between 65% and 100% of the initial one, in the presence of pulp. The pulp was found to protect the enzyme against inactivation: the activity was only reduced by 45% in its presence. Under the operating conditions used the natural mediators proved less efficient than HBT in facilitating pulp bleaching; rather, they tended to bind to pulp fibres. This effect could be used to functionalize fibres in order to improve intrinsic properties of pulp or introducing novel ones (e.g. antimicrobial, antioxidant, optical properties, etc.). This paper shows for the first time the application of laccase-mediator systems to sisal pulp.
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PMID:Application of laccase-natural mediator systems to sisal pulp: an effective approach to biobleaching or functionalizing pulp fibres? 1957 42

The interactions between two oxidoreductases coupled by an artificial redox mediator have been described quantitatively to increase both stability and productivity. In this cascade oxidation, pyranose 2-oxidase oxidizes several aldoses at the C-2 position to 2-ketoaldoses. A redox mediator is used as electron acceptor for pyranose 2-oxidase because it shows more favourable kinetics in comparison to oxygen. The reduced redox mediator is in turn re-oxidized by laccase, which uses oxygen as the terminal electron acceptor, reducing it fully to water. However, pyranose 2-oxidase is capable of using oxygen as an electron acceptor in a competing side reaction, leading to the formation of hydrogen peroxide, which is detrimental for both enzymes and seriously limits the operational stability of both enzymes. The experimental results showed full conversion of the aldose to the 2-ketoaldose and a good agreement with the simulations of the process.
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PMID:Biocatalytic cascade oxidation using laccase for pyranose 2-oxidase regeneration. 1959 89

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

This study evaluates the bleaching efficiency of enzymatically scoured linen fabrics using a combined laccase-hydrogen peroxide bleaching process with and without ultrasonic energy, with the goal of obtaining fabrics with high whiteness levels, well preserved tensile strength and higher dye uptake. The effect of the laccase enzyme and the combined laccase-hydrogen peroxide bleaching process with and without ultrasound has been investigated with regard to whiteness value, tensile strength, dyeing efficiency and dyeing kinetics using both reactive and cationic dyes. The bleached linen fabrics were characterized using X-ray diffraction and by measuring tensile strength and lightness. The dyeing efficiency and kinetics were characterized by measuring dye uptake and colour fastness. The results indicated that ultrasound was an effective technique in the combined laccase-hydrogen peroxide bleaching process of linen fabrics. The whiteness values expressed as lightness of linen fabrics is enhanced by using ultrasonic energy. The measured colour strength values were found to be slightly better for combined laccase-hydrogen peroxide/ultrasound-assisted bleached fabrics than for combined laccase-hydrogen peroxide for both reactive and cationic dyes. The fastness properties of the fabrics dyed with reactive dye were better than those obtained when using cationic dye. The time/dye uptake isotherms were also enhanced when using combined laccase-hydrogen peroxide/ultrasound-assisted bleached fabric, which confirms the efficiency of ultrasound in the combined oxidative bleaching process. The dyeing rate constant, half-time of dyeing and dyeing efficiency have been calculated and discussed.
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PMID:Ecofriendly laccase-hydrogen peroxide/ultrasound-assisted bleaching of linen fabrics and its influence on dyeing efficiency. 1974 14

The C-terminus of the fungal laccase from Melanocarpus albomyces (MaL) is processed during secretion at a processing site conserved among the ascomycete laccases. The three-dimensional structure of MaL has been solved as one of the first complete laccase structures. According to the crystal structure of MaL, the four C-terminal amino acids of the mature protein penetrate into a tunnel leading towards the trinuclear site. The C-terminal carboxylate group forms a hydrogen bond with a side chain of His140, which also coordinates to the type 3 copper. In order to analyze the role of the processed C-terminus, site-directed mutagenesis of the MaL cDNA was performed, and the mutated proteins were expressed in Trichoderma reesei and Saccharomyces cerevisiae. Changes in the C-terminus of MaL caused major defects in protein production in both expression hosts. The deletion of the last four amino acids dramatically affected the activity of the enzyme, as the deletion mutant delDSGL(559) was practically inactive. Detailed characterization of the purified L559A mutant expressed in S. cerevisiae showed the importance of the C-terminal plug for laccase activity, stability, and kinetics. Moreover, the crystal structure of the L559A mutant expressed in S. cerevisiae showed that the C-terminal mutation had clearly affected the trinuclear site geometry. The results in this study clearly confirm the critical role of the last amino acids in the C-terminus of MaL.
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PMID:Essential role of the C-terminus in Melanocarpus albomyces laccase for enzyme production, catalytic properties and structure. 1978 Aug 17

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

Electrodes modified with sol-gel encapsulated laccase (isolated from Cerrenaunicolor) exhibiting mediated or mediatorless bioelectrocatalytic dioxygen reduction activity were inspected using confocal laser scanning microscopy, atomic force microscopy and scanning electrochemical microscopy. Potential-driven leaching of the redox mediator 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) from carbon ceramic electrodes covered by hydrophilic silicate-encapsulated laccase was detected during electrocatalytic action. Strongly non-homogeneous lateral distribution of the activity towards dioxygen reduction was found by redox competition mode of scanning electrochemical microscopy using a similar electrode with syringaldazine as redox mediator. Hydrogen peroxide formation at these electrodes is detected at potentials lower than 0.05V. It is ascribed to the electrochemical oxygen reduction at the carbon material while laccase-catalyzed oxygen reduction occurs below 0.35V without hydrogen peroxide formation. The scanning electrochemical microscopy images of electrodes consisting of single-walled carbon nanotubes non-covalently modified with pyrenesulfonate and laccase encapsulated in a sol-gel processed silicate film confirm direct electron transfer electrocatalysis in redox competition mode experiments and show that the enzyme is evenly distributed in the composite film. In conclusion scanning electrochemical microscopy proved to be useful for mapping of enzyme activity on different materials.
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PMID:Scanning electrochemical microscopy activity mapping of electrodes modified with laccase encapsulated in sol-gel processed matrix. 2009 39

The phenols syringaldehyde (SA), acetosyringone (AS) and p-coumaric acid (PCA) were used as natural laccase mediators in combination with a laccase from Pycnoporus cinnabarinus to bleach flax fibres. Their performance was compared with 1-hydroxybenzotriazole (HBT) in terms of enzyme stability, and pulp and effluent properties. HBT and PCA were found to inactivate laccase in the absence of pulp. However, in the presence of unbleached flax pulp stability was increased; for example with PCA, laccase retained 77% of its initial activity, in contrast with complete inactivation in the absence of pulp. This suggests a protective effect of the pulp against denaturalization of the enzyme. All natural mediators resulted in a reduced kappa number after the subsequent alkaline treatment with hydrogen peroxide; the reduction being especially marked with SA (about 2 units - with respect to the control sample) and comparable to that obtained by HBT. Brightness was significantly increased by all natural mediators, but especially by AS and SA (23% with both), which performed very similarly to HBT in this respect. Natural mediators therefore might constitute an effective alternative to synthetic mediators for flax pulp biobleaching. This paper demonstrates for the first time the use of natural mediators in the laccase-assisted delignification of flax pulp and their effect on the properties of the resulting effluents.
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PMID:A new approach to the biobleaching of flax pulp with laccase using natural mediators. 2013 56

Dihydrolipoamide dehydrogenase (LPD), a useful biocatalyst for regenerating NAD(+), was purified from Microbacterium luteolum JCM 9174, and the gene encoding LPD was cloned from the genomic DNA. The gene contained an opening reading frame consisting of 1395 nucleotides encoding 465 amino acid residues with a predicted molecular weight of 49912.1 Da, which displayed 36-78% homology to known LPDs. Moreover, the FAD- and NAD(+)-binding sites and the two catalytic residues in the LPDs were conserved. The enzyme was expressed in recombinant Escherichia coli cells and purified to homogeneity by column chromatography. LPD of M. luteolum (MluLPD) accepted not only lipoamide but also some artificial electron acceptors such as dichlorophenolindophenol (DCIP) and nitrotetrazolium blue (NTB), that is, it functions as a diaphorase. NAD(+) demonstrated a strong activating effect on MluLPD, and the activity was 5.2 times higher than that without NAD(+). The enzyme was suitable for regenerating NAD(+) in biocatalytic reactions because of its high affinity for NADH (6.1 microM). An NAD(+)-regenerating system with MluLPD and laccase using 2,5-dimethoxy-1,4-benzoquinone as a hydrogen acceptor was demonstrated.
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PMID:Gene cloning and characterization of dihydrolipoamide dehydrogenase from Microbacterium luteolum: A useful enzymatic regeneration system of NAD+ from NADH. 2015 66

Three extracellular ligninolytic oxidoreductases that are produced by a commercial laccase-producing Trametes sp. Ha1 were purified and characterized. This fungus showed strong ligninolytic oxidoreductase activity with and without hydrogen peroxide present in the reaction mixture. The oxidoreductase activity was found to be derived from two laccases and a peroxidase. One of the two laccases represents a main component of the commercial laccase preparation from Trametes sp. Ha1. This enzyme had a high thermostability, which makes it attractive for practical applications. The second laccase was induced by the addition of p-xylidine into the culture medium and showed unique characteristics with respect to pI value and substrate specificity. The peroxidase showed wide oxidation activity against aromatic compounds.
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PMID:Two laccase isoenzymes and a peroxidase of a commercial laccase-producing basidiomycete, Trametes sp. Ha1. 2018 74


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