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)

Tyrosinase, which is known to possess both monophenol monooxygenase activity (EC 1.14.18.1, tyrosine, 3,4-dihydroxyphenylalanine:oxygen oxidoreductase) and o-diphenoloxidase activity (EC 1.10.3.1, o-diphenol:oxygen oxidoreductase), has been shown to exhibit other related activities. Recently, a new reaction, viz., oxidative conversion of 2,6-dimethoxyallyl phenol to its quinone methide, catalyzed by commercial preparations of mushroom tyrosinase was reported (E. S. Krol, and J. L. Bolton, 1997, Chem. Biol. Interact. 104, 11-27). Since the reaction involves an unusual 1,6-oxidation rather than the conventional 1,4-oxidation, we reexamined this reaction more carefully. The o-diphenoloxidase activity and the dimethoxyallyl phenol oxidase activity of mushroom tyrosinase preparations exhibited different mobilities on size-exclusion chromatography on a Sephacryl S-200 column. A similar behavior was also witnessed on preparative isoelectric focusing in a rotofor cell. Different preparations of mushroom tyrosinase possessed varying ratios of these two activities, further confirming that they are due to two different enzymes. Native polyacrylamide gel electrophoresis followed by activity staining of the gel revealed different mobilities for these two activities. The protein band exhibiting dimethoxyallyl phenol oxidase activity could also be stained by syringaldazine, a well-known substrate for laccase (EC 1.10.3.2, p-diphenol:oxygen oxidoreductase). Two insect phenoloxidases, which are known for their wide substrate specificity, failed to oxidize dimethoxyallyl phenol to any detectable extent, thereby confirming that typical o-diphenoloxidases lack the ability to oxidize dimethoxyallyl phenol. On the other hand, laccase, which is known to convert syringaldazine to its quinone methide derivative, readily produced the quinone methide from dimethoxyallyl phenol. It is therefore concluded that laccase, which is present as a contaminant in the commercial preparations of mushroom tyrosinase--and not tyrosinase (o-diphenoloxidase)--is the enzyme responsible for catalyzing the new conversion of dimethoxyallyl phenol to its corresponding quinone methide.
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PMID:Laccase--and not tyrosinase--is the enzyme responsible for quinone methide production from 2,6-dimethoxy-4-allyl phenol. 960 54

The white-rot fungus Trametes trogii excretes a main laccase showing a molecular mass of 70 kDa, acidic isoelectric point and N-terminal sequence homologous to that of several phenol oxidases. The purified enzyme oxidizes a number of phenolic and non-phenolic compounds; recalcitrant molecules may be converted into substrates by introducing, in the correct position, o- or p-orienting ring-activating groups.
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PMID:Laccase from the white-rot fungus Trametes trogii. 965 Feb 52

A Myceliophthora thermophila laccase and a Rhizoctonia solani laccase were mutated on a pentapeptide segment believed to be near the type-1 Cu site. The mutation L513F in Myceliophthora laccase and the mutation L470F in Rhizoctonia laccase took place at a position corresponding to the type-1 Cu axial methionine (M517) ligand in Zucchini ascorbate oxidase. The triple mutations V509L,S510E,G511A in Myceliophthora laccase and L466V,E467S,A468G in Rhizoctonia laccase involved a sequence segment whose homologue in ascorbate oxidase is flanked by the M517 and a type-1 Cu-ligating histidine (H512). The single mutation did not yield significant changes in the enzymic properties (including any significant increase in the redox potential of the type-1 Cu). In contrast, the triple mutation resulted in several significant changes. In comparison with the wild type, the Rhizoctonia and Myceliophthora laccase triple mutants had a phenol-oxidase activity whose pH optimum shifted 1 unit lower and higher, respectively. Although the redox potentials were not significantly altered, the Km, kcat and fluoride inhibition of the laccases were greatly changed by the mutations. The observed effects are interpreted as possible mutation-induced structural perturbations on the molecular recognition between the reducing substrate and laccase and on the electron transfer from the substrate to the type-1 Cu centre.
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PMID:Site-directed mutations in fungal laccase: effect on redox potential, activity and pH profile. 969 3

Two isoforms of laccase were obtained as the predominant phenol-oxidases in defined medium liquid cultures of the "white-rot" fungus Rigidoporus lignosus (R. lignosus). A characterization of the two laccases was made in terms of molecular mass, isoelectric point, metal content and N-terminal sequence. Furthermore, in order to gain information on the structural features related to the metal centers, a study of their geometric arrangement and their redox ability was made. It turned out that the two isoenzymes greatly differed with regard to pH stability, catalytic and copper centers features. It is proposed that all such differences are dependent on the amino acid sequences, which cause a distortion of the copper sites, thus accounting for the redox potential values and kinetic properties.
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PMID:A comparative study of two isoforms of laccase secreted by the "white-rot" fungus Rigidoporus lignosus, exhibiting significant structural and functional differences. 983 27

The white-rot fungus Trametes versicolor was used to study the influence of extracellular laccase activity on the degradation of 2-chlorophenol (2-CP) and the formation of metabolites under conditions, characterized by the absence of other phenol-oxidizing enzymes. 2-CP enhanced the production of extracellular laccase by fungal mycelia. The formation of the metabolite 2-chloro-1,4-benzoquinone (2-CIBQ) was found to be correlated with extracellular laccase activity. In cell-free crude culture liquids laccase was responsible for the oxidation of 2-CP. In contrast to this, the disappearance of 2-CP caused by the entire organism did not correlate with extracellular laccase activity. The primary oxidative step during the degradation of this compound can thus only partially be attributed to extracellular laccase; indicating the involvement of cell-bound processes.
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PMID:Degradation of 2-chlorophenol and formation of 2-chloro-1,4-benzoquinone by mycelia and cell-free crude culture liquids of Trametes versicolor in relation to extracellular laccase activity. 987 33

Several fungal laccases have been compared for the oxidation of a nonphenolic lignin dimer, 1-(3, 4-dimethoxyphenyl)-2-(2-methoxyphenoxy)propan-1,3-diol (I), and a phenolic lignin model compound, phenol red, in the presence of the redox mediators 1-hydroxybenzotriazole (1-HBT) or violuric acid. The oxidation rates of dimer I by the laccases were in the following order: Trametes villosa laccase (TvL) > Pycnoporus cinnabarinus laccase (PcL) > Botrytis cinerea laccase (BcL) > Myceliophthora thermophila laccase (MtL) in the presence of either 1-HBT or violuric acid. The order is the same if the laccases are used at the same molar concentration or added to the same activity (with ABTS [2, 2'-azinobis (3-ethylbenzothiazoline-6-sulfonic acid)] as a substrate). During the oxidation of dimer I, both 1-HBT and violuric acid were to some extent consumed. Their consumption rates also follow the above order of laccases, i.e., TvL > PcL > BcL > MtL. Violuric acid allowed TvL and PcL to oxidize dimer I much faster than 1-HBT, while BcL and violuric acid oxidized dimer I more slowly than BcL and 1-HBT. The oxidation rate of dimer I is dependent upon both kcat and the stability of the laccase. Both 1-HBT and violuric acid inactivated the laccases, violuric acid to a greater extent than 1-HBT. The presence of dimer I or phenol red in the reaction mixture slowed down this inactivation. The inactivation is mainly due to the reaction of the redox mediator free radical with the laccases. We did not find any relationship between the carbohydrate content of the laccases and their inactivation. When the redox potential of the laccases is in the range of 750 to 800 mV, i.e., above that of the redox mediator, it does not affect kcat and the oxidation rate of dimer I.
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PMID:Comparison of fungal laccases and redox mediators in oxidation of a nonphenolic lignin model compound. 1034 57

The oxidation of polycyclic aromatic compounds was studied in systems consisting of laccase from Trametes versicolor and so-called mediator compounds. The enzymatic oxidation of acenaphthene, acenaphthylene, anthracene, and fluorene was mediated by various laccase substrates (phenols and aromatic amines) or compounds produced and secreted by white rot fungi. The best natural mediators, such as phenol, aniline, 4-hydroxybenzoic acid, and 4-hydroxybenzyl alcohol were as efficient as the previously described synthetic compounds ABTS [2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid)] and 1-hydroxybenzotriazole. The oxidation efficiency increased proportionally with the redox potentials of the phenolic mediators up to a maximum value of 0.9 V and decreased thereafter with redox potentials exceeding this value. Natural compounds such as methionine, cysteine, and reduced glutathione, containing sulfhydryl groups, were also active as mediator compounds.
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PMID:Natural mediators in the oxidation of polycyclic aromatic hydrocarbons by laccase mediator systems. 1065 13

One-electron oxidation activity, as measured by ethylene generation from 2-keto-4-thiomethylbutyric acid, phenol oxidase activity, and the generation of hydroxyl radical were examined in cultures of the lignin-degrading white-rot basidiomycete fungus, Trametes (Coriolus) versicolor. The activity levels of specific lignin-degrading enzymes and cellulases, as well as the rate of wood degradation, also were examined. The fungus secreted a low-molecular-weight substance (M(r) 1000-5000) that catalyzed a redox reaction between molecular oxygen and an electron donor, to produce the hydroxyl radical via hydrogen peroxide. During wood decay, T. versicolor also produced significant amounts of laccase and lignin peroxidase, carboxymethyl cellulase, and Avicelase. The roles of the hydroxyl radical, phenol oxidases, and cellulases in wood degradation by white-rot fungi are discussed. That the hydroxyl radical produced by the low-molecular-weight substance secreted by T. versicolor results in new phenolic substructures on the lignin polymer, making it susceptible to attack by laccase or manganese peroxidase is suggested.
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PMID:Hydroxyl radical generation by an extracellular low-molecular-weight substance and phenol oxidase activity during wood degradation by the white-rot basidiomycete Trametes versicolor. 1070 93

Samples of South Vietnamese soils intensely treated with Agent Orange defoliant were tested for the presence of fungi and actinomycetes with elevated phenol oxidase activity. As a result, fast-growing non-sporulating strain producing neutral phenol oxidases was isolated and identified as Mycelia sterilia INBI 2-26. The strain formed extracellular phenol oxidases during surface growth on liquid medium in the presence of guayacol and copper sulfate, as well as during submerged cultivation in liquid medium containing wheat bran and sugar beet pulp. Isoelectric focusing of cultural liquid has revealed two major catechol oxidases (PO1 and PO2) with pI 3.5 and 8, respectively. The enzymes were purified by ultrafiltration, ion exchange chromatography and exclusion HPLC. Both were stable between pH 3 and 8. At pH 8 and 40 degrees C they retained at least 50% of activity after incubation for 50 h. At 50 degrees C PO2 was more stable and retained 40% of activity after 50 h, whereas PO1 was inactivated in 3-6 h. The pH optimums for PO1 and PO2 towards catechol were equal to 6 and 6.5, and the Km values were 1.5 +/- 0.35 and 1.25 +/- 0.2 mM, respectively. PO1 and PO2 most optimally oxidized 2,2'-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid) at pH 3 with Km values 1.6 +/- 0.18 and 0.045 +/- 0.01 mM, respectively, but displayed no activity towards tyrosine. The PO2 absorbance spectrum had a peak at 600 nm, thus indicating the enzyme to be a member of the laccase family.
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PMID:[Isolation and characteristics of micromycetes--producers of neutral phenol oxidase from trophic soil with a high level of dioxins]. 1099 89

Initiation of copolymerization of lignin-like phenolic and acrylic compounds by the phenoloxidase laccase (EC 1.10.3.2) and a peroxide species (t-butylhydroperoxide, t-BHP) was compared to a Fenton-like system (ferrous ion, t-BHP). Initially, the relative activity of laccase towards different phenolic compounds and the optimum pH of some characteristic phenolics were determined. The polymer yield and the average molecular weight (Mw) of chemo-enzymatically produced polymers were dependent both on the type of each phenolic tested and on the phenol/monomer ratio. Furthermore, the success of copolymerization of the phenolics was dependent both on their redox potential and on the type of acrylic monomer applied. The extent of phenol incorporation into the polymer chain was enhanced by the presence of laccase in the reaction mixture and was significantly higher than in polymerization initiated by a Fenton-like reaction.
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PMID:Chemo-enzymatically induced copolymerization of phenolics with acrylate compounds. 1133 Jul 11


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