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)

1. Recent magnetic susceptibility measurements on laccase (monophenol,dihydroxyphenylalanine:oxygen oxidoreductase, EC 1.14.18.1) from the lacquer tree Rhus vernicifera showed a deviation from Curie behaviour above 50 K, which was taken as evidence for an antiferromagnetically coupled Cu(II)-Cu(II) pair in the oxidized enzyme. The magnetic susceptibility of this protein has been reinvestigated. Further measurements on laccase from the fungus Polyporus versicolor and human ceruloplasmin (iron(II):oxygen oxidoreductase, EC 1.16.3.1) are presented. 2. The magnetic susceptibility of fungal laccase and lacquer tree laccase can be accounted for by the EPR detectable copper ions in the temperature range 40--300 K. 3. If an antiferromagnetically coupled Cu(II)-Cu(II) pair exists in the laccases, then the coupling, expressed as --J, should be at least of the order of 300 cm-1, as deduced from the Curie dependence of the susceptibility and the sensitivity in our measurements. 4. If an analogy with the laccases is assumed for the EPR invisible copper in ceruloplasmin then a limiting value of the coupling may be deduced also in this case, with --J at least of the order of 200 cm-1.
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PMID:Magnetic susceptibility of laccases and ceruloplasmin. 21 24

Rate constants have been determined for the electron-transfer reactions between reduced horse heart cytochrome c and resting Rhus vernicifera laccase as a function of pH, ionic strength, and temperature. The second-order rate constant for the oxidation of reduced cytochrome c was determined to be k = 125 M-1 s-1 at 25 degrees C in 0.2 M phosphate buffer at pH 6.0 with the activation parameters delta H++ = 16.2 kJ mol-1 and delta S++ = 28.9 J mol-1 K-1. The rate constants increased with decreasing buffer concentration, indicating that electron transfer from cytochrome c to laccase is favored by the local electrostatic interaction (ZAZB = -0.9 at pH 6 and -1.3 at pH 4.8) between the basic proteins with positive net charges. From the increase of the rate of electron transfer with decreasing pH, one of the driving forces of the reaction was suggested to be the difference in the redox potentials between the type 1 copper in laccase and the central iron in cytochrome c. Further, on addition of one hexametaphosphate anion per cytochrome c molecule, the rate of the electron transfer was increased, probably because the association of both proteins became more favorable.
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PMID:Kinetics of electron transfer between cytochrome c and laccase. 132 27

We report results of experiments designed to characterize the Type 1 and Type 3 copper sites in Rhus laccase depleted of Type 2 copper (T2D). Use of the Lowry method for determining protein concentration yielded the value 5620 +/- 570 M-1 cm-1 for the extinction of the 615-nm absorption band of this protein. Anaerobic reductive titrations with Ru(NH)3)6(2)+ and Cr(II)aq ions established the presence of three electron-accepting centers, which are reduced in a complex manner. Treatment of T2D laccase with a 70-fold excess of H2O2 induced a new shoulder at 330 nm (delta epsilon = 660 M-1 cm-1), as well as intensity perturbations at 280 and 615 nm. Comparison of difference spectra show that this 330-nm band derives from a Type 3 copper-bound peroxide and not from a reoxidized Type 3 site. Dioxygen reoxidation of ascorbate-reduced T2D laccase produced new difference bands at 330 nm (delta epsilon = 770 M-1 cm-1) and 270 nm (delta epsilon = 13,000 M-1 cm-1), the former assigned to a bound peroxide which is a dioxygen reduction intermediate. In the corresponding epr spectrum of this material new Cu(II) g parallel features (A parallel approximately 130 G) indicative of an isolated copper ion and a triplet signal near 3,400 G were observed, originating from the Type 3 sites of separate T2D laccase molecules. Reoxidation by ferricyanide or by dioxygen as mediated by iron hexacyanide did not produce these changes. Thus the magnetism of the reoxidized Type 3 site in T2D laccase can be perturbed as a consequence of aerobic turnover. The suggestion is advanced that there are presently three forms of T2D laccase, possibly metastable conformational isotypes, accounting for the apparently contradictory reports on the properties of this protein.
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PMID:The Type 3 copper site is intact but labile in Type 2-depleted laccase. 630 31

Two laccase isoenzymes (POXA1 and POXA2) produced by Pleurotus ostreatus were purified and fully characterized. POXA1 and POXA2 are monomeric glycoproteins with 3 and 9% carbohydrate content, molecular masses of about 61 and 67 kDa by sodium dodecyl sulfate polyacrylamide gel electrophoresis, of about 54 and 59 kDa by gel filtration in native conditions, and of 61 kDa by matrix-assisted laser desorption ionization mass spectrometry (only for POXA1) and pI values of 6.7 and 4.0, respectively. The N terminus and three tryptic peptides of POXA1 have been sequenced, revealing clear homology with laccases from other microorganisms, whereas POXA2 showed a blocked N terminus. The stability of POXA2 as a function of temperature was particularly low, whereas POXA1 showed remarkable high stability with respect to both pH and temperature. Both enzymes oxidize syringaldazine and ABTS (2, 2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)) together with a variety of different substituted phenols and aromatic amines with the concomitant reduction of oxygen, but POXA1 is unable to oxidize guaiacol. Both enzymes were strongly inhibited by sodium azide and thioglycolic acid but not by EDTA. UV/visible absorption spectra, atomic adsorption, and polarographic data indicated the presence of 4 copper atoms/mol of POXA2 but only one copper, two zinc, and one iron atoms were found/mol of POXA1. The neutral pI and the anomalous metal content of POXA1 laccase render this enzyme unique in its structural characteristics. The lack of typical absorbance at 600 nm allows its classification as a "white" laccase.
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PMID:A novel white laccase from Pleurotus ostreatus. 939 57

A new laccase isoenzyme (POXA1b, where POX is phenol oxidase), produced by Pleurotus ostreatus in cultures supplemented with copper sulphate, has been purified and fully characterized. The main characteristics of this protein (molecular mass in native and denaturing conditions, pI and catalytic properties) are almost identical to the previously studied laccase POXA1w. However, POXA1b contains four copper atoms per molecule instead of one copper, two zinc and one iron atom per molecule of POXA1w. Furthermore, POXA1b shows an unusually high stability at alkaline pH. The gene and cDNA coding for POXA1b have been cloned and sequenced. The gene coding sequence contains 1599 bp, interrupted by 15 introns. Comparison of the structure of the poxa1b gene with the two previously studied P. ostreatus laccase genes (pox1 and poxc) suggests that these genes belong to two different subfamilies. The amino acid sequence of POXA1b deduced from the cDNA sequence has been almost completely verified by means of matrix-assisted laser desorption ionization MS. It has been demonstrated that three out of six putative glycosylation sites are post-translationally modified and the structure of the bound glycosidic moieties has been determined, whereas two other putative glycosylation sites are unmodified.
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PMID:Protein and gene structure of a blue laccase from Pleurotus ostreatus1. 1041 29

While laccase of Cryptococcus neoformans is implicated in the virulence of the organism, our recent studies showing absence of melanin in the infected mouse brain has led us to a search for alternative roles for laccase in cryptococcosis. We investigated the role of laccase in protection of C. neoformans against murine alveolar macrophage (AM)-mediated antifungal activity by using a pair of congenic laccase-positive (2E-TUC) and laccase-deficient (2E-TU) strains. The laccase-positive cells with laccase derepression were more resistant to the antifungal activity of AM than a laccase-deficient strain ([28.9 +/- 1.2]% versus [40.2 +/- 2.6]% killing). Addition of L-dopa to Cryptococcus to produce melanin in a laccase-positive strain resulted in a slight increase in protection of C. neoformans from the antifungal activity of macrophages ([25.4 +/- 3.4]% versus [28.9 +/- 1.2]% killing). Recombinant cryptococcal laccase exhibited iron oxidase activity in converting Fe(II) to Fe(III). Moreover, recombinant laccase inhibited killing of C. neoformans by hydroxyl radicals catalyzed by iron in a cell-free system. Addition of the hydroxyl radical scavenger mannitol or dimethyl sulfoxide to AMs prior to the introduction of cryptococcal cells decreased killing of both strains and reduced the difference in susceptibility between the laccase-positive and laccase-deficient strains. Furthermore, laccase-mediated protection from AM killing was inhibited by the addition of Fe(II), presumably by overcoming the effects of the iron oxidase activity of cryptococcal laccase. These results suggest that the iron oxidase activity of laccase may protect C. neoformans from macrophages by oxidation of phagosomal iron to Fe(III) with a resultant decrease in hydroxyl radical formation.
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PMID:Laccase protects Cryptococcus neoformans from antifungal activity of alveolar macrophages. 1053 Dec 64

The effect of different ions which are constituents of technical lignin sulfonates (LS) on chemo-enzymatic graft co-polymerization was determined. The application of the iron chelator desferrioxamine in the initial reaction mixture revealed that iron impurities of LS which catalyzed a Fenton-like reaction were crucial for the initiation of grafting, whereas calcium or chloride ions showed no such effect. The addition of laccase (ATCC 11235) to the reaction mixture which contained desferrioxamine caused a significantly higher yield compared to the control; this indicates a crucial effect of laccase with regard to the initiation of copolymerization. The involvement of laccase in the initiation of the graft copolymerization was additionally confirmed by the application of low molecular weight phenolics instead of LS. In the presence of the lignin-like substrates, 3,4-dihydroxybenzoic acid and guaiacol, the rate of the decomposition of t-butylhydroperoxide was significantly enhanced by laccase. It can be assumed that the enzymatically generated phenoxy radicals mediate the production of oxygen centered radicals (alkoxy or peroxy) which initiate grafting.
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PMID:The effect of ions on the enzymatically induced synthesis of lignin graft copolymers. 1124 Feb 6

Virulence is the outcome of an interaction between the host and a microbe and is characterized by a large array of opposing reactions operating at the host-pathogen interface. Cryptococcus neoformans is an important opportunistic pathogen in immunocompromised patients, including those with human immunodeficiency virus, and expresses a virulence-associated laccase which is believed to oxidize brain catecholamines and iron as a defense against host immune cells. In the present report, we investigated the cellular location of laccase to understand more fully how it contributes to cryptococcal virulence. A monoclonal antibody to the C. neoformans laccase was generated and used to show localization in the cell walls of representative serotype A (H99) and serotype D (B-3501) strains by immunoelectron microscopy. In addition, confocal microscopy was used to show a peripheral location of green fluorescent protein-tagged laccase expressed in live H99 cells. Biochemical studies showed that laccase could be released from intact cells or cell wall fractions with glucanase enzymes but was retained in the cell wall after sequential extraction with 1 M NaCl, 6 M urea, and 1% sodium dodecyl sulfate. The presence of a hydrolyzable bond linking laccase to the cell wall was suggested by removal of laccase from cell wall preparations after they were boiled in 1% sodium dodecyl sulfate, as was the presence of a disulfide or thioester bond by removal with dithiothreitol or beta-mercaptoethanol. These data show that laccase is present as a tightly associated cell wall enzyme that is readily accessible for interactions with host immune cells.
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PMID:Laccase of Cryptococcus neoformans is a cell wall-associated virulence factor. 1150 Apr 33

2,6-Dimethoxyphenol is a versatile substrate for Pyricularia oryzae laccase, PpoA from Marinomonas mediterranea, phenoxazinone synthase from Streptomyces antibioticus and mammalian ceruloplasmin. In addition, in cellular extracts of microorganisms expressing other blue multicopper proteins with no enzymatic activity previously described, such as Escherichia coli (copper resistance CueO), Pseudomonas syringae and Xanthomonas campestris (copper resistance CopA), Bacillus subtilis (sporulation protein CotA) and Saccharomyces cerevisiae (iron transporter Fet3p), laccase activity is detected under appropriate conditions. This oxidase activity can be spectrophotometrically followed by the oxidation of 2,6-dimethoxyphenol. Specific staining after SDS-PAGE is also possible for some of these proteins. This detection assay can facilitate the study of the multiple functions that such proteins seem to carry out in a variety of microorganisms.
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PMID:Dimethoxyphenol oxidase activity of different microbial blue multicopper proteins. 1168 98

This study was performed to determine which oxidoreductive catalysts were most efficient in catalyzing the binding of 8-hydroxybentazon to soil humic substances. 8-Hydroxybentazon was completely transformed by an oxidoreductive enzyme, laccase of Myceliophthora thermophila, at pH 3.0-7.0 within 30 min. When abiotic catalysts, manganese(IV), iron(III), and aluminum oxides were used in the same pH range, 8-hydroxybentazon was completely transformed only by manganese(IV) oxide (delta-MnO2), but a relatively small amount of 8-hydroxybentazon was transformed by iron(III) oxide and aluminum oxide. The adsorption of 8-hydroxybentazon in the soil showed an H-type and coincided well with the Langmuir isotherm. To better understand the factors involved in the rapid and strong binding of 8-hydroxybentazon with soil humic substances, 8-hydroxybentazon transformation by oxidoreductive catalysts was studied in various soil conditions: air-dried, preincubated, sterilized, and iron(III) oxide and manganese(IV) oxide free. 8-Hydroxybentazon was completely transformed within 24 h in the decreasing order of preincubated, air-dried, and sterilized soils. However, little transformation was observed in the iron(III) oxide and manganese(IV) oxide free soils. These results suggest that the major catalyst responsible for the rapid and strong binding of 8-hydroxybentazon to soil humic substances is a metal oxide, manganese(IV) oxide, not a soil oxidoreductive enzyme.
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PMID:Formation of bound residues of 8-hydroxybentazon by oxidoreductive catalysts in soil. 1203 19


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