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)

Monophenol monooxygenase (monophenol, dihydroxyphenylalanine:oxygen oxidoreductase EC 1.14.18.1) was studied in melanin-positive and melanin-negative mutants of Streptomyces lincolnensis NCIB 9413, varying in the lincomycin synthesizing ability. The activities of laccase and tyrosine phenol lyase (EC 4.1.99.2) are absent in this organism. The monophenol monooxygenase catalyzes hydroxylation of monophenols (K(m) and V(max) for l-tyrosine, 2 x 10(-4) M and 8.0 nmol of O(2)/min per ml, respectively) at a slower rate than it dehydrogenates diphenols to o-quinones (K(m) and V(max) for l-3,4-dihydroxyphenylalanine, 7 x 10(-5) M and 51.7 nmol of O(2)/min per ml, respectively. It is inhibited by KCN, beta-mercaptoethanol, ethylenediaminetetraacetate, dipyridyl, thiourea, p-aminobenzoic acids and by some tryptophan metabolites. Changes in the activity of monophenol monooxygenase caused by mutation or by inhibitors are reflected in the synthesis of the antibiotic. Its participation in the biogenesis of the propylhygric moiety of lincomycin is discussed.
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PMID:Monophenol monooxygenase and lincomysin biosynthesis in Streptomyces lincolnensis. 81 70

The culture of Streptomyces galbus ISP-5089 has a yellow-green colour caused by the accumulation of actinomycin X when it is grown in synthetic media at 28 degrees C; the colour turns dark-brown at 42 degrees C due to the synthesis of melanoid pigments. The population composition does not undergo any noticeable changes in that case, an no specific melanin-synthesizing mutants appear as a result of autoselection . The biosynthesis of actinomycin X (at 28 degrees C) and melanoid pigments (at 42 degrees C) is regulated by temperature. At 42 degrees C, L-DOPA oxidase is synthesized and laccase is activated; these two enzymes are involved in the synthesis of melanoid pigments. The organism does not has tyrosinase. The synthesis of melanoid pigments, when the mesophilic culture of S. galbus ISP-5089 is grown in the regime of superoptimal temperatures (42 to 47 degrees C), may be considered as a protective ecological reaction of the organism to unfavourable conditions of the environment.
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PMID:[Nature of the brown pigment and the composition of the phenol oxidases of Streptomyces galbus]. 620 87

3,4-Dihydroxyphenylalanine (DOPA) is not a preferred substrate of Rhus vernicifera laccase, as rate constants for the anaerobic reduction of the type 1 cupric atom by L-DOPA (6.3 X 10(1) M-1 s-1), D-DOPA (2.6 X 10(1) M-1 s-1), and L-DOPA methyl ester (2.6 X 10(1) M-1 s-1) are considerably smaller than k1 (catechol) (7 X 10(2) M-1 s-1) and rate constants characteristic of numerous other nonphysiological organic substrates (25 degrees C, pH 7.0, I = 0.5 M). The reactions of DOPA derivatives with laccase are unique, however, in that a two-term rate law pertains: kobsd = k0 + k1[phenol]; k0(L-DOPA) = 7 X 10(-2) s-1. The reactivities of other catechol derivatives (pyrogallol, gallic acid, and methyl gallate) with laccase type 1 copper were also examined.
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PMID:Reduction of laccase type 1 copper by 3,4-dihydroxyphenylalanine and other catechol derivatives. 622 99

Pigment production by Cryptococcus neoformans is virulence associated. Dopamine- and 3,4-dihydroxyphenylalanine-melanin products were identified after acidic permanganate oxidation, alkaline hydrogen peroxide oxidation, or hydrolysis with hydriodic acid. These data provide direct chemical evidence for the formation of eumelanin polymers by catecholamine oxidation by laccase alone followed by oxidative coupling of dihydroxyindole.
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PMID:Melanin biosynthesis in Cryptococcus neoformans. 951 29

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

Eumelanins in animals are biosynthesized by the combined action of tyrosinase, 3,4-dihydroxyphenylalanine (DOPA)chrome isomerase, and other factors. Two kinds of eumelanins were characterized from mammalian systems; these are 5,6-dihydroxyindole (DHI)-melanin and 5,6-dihydroxyindole-2-carboxylic acid (DHICA)-melanin. In insects, melanin biosynthesis is initiated by phenoloxidase and supported by DOPAchrome isomerase (decarboxylating). Based on the facts that DOPA is a poor substrate for insect phenoloxidases and DHI is the sole product of insect DOPAchrome isomerase reaction, it is proposed that insects lack DHICA-melanin. Accordingly, the phenoloxidase isolated from the hemolymph of Manduca sexta failed to oxidize DHICA. Control experiments reveal that mushroom tyrosinase, as well as laccase, which is a contaminant in the commercial preparations of mushroom tyrosinase, are capable of oxidizing DHICA. Neither the whole hemolymph nor the cuticular extracts of M. sexta possessed any detectable oxidase activity towards this substrate. Thus, insects do not seem to produce DHICA-eumelanin. A useful staining procedure to localize DHICA oxidase activity on gels is also presented.
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PMID:Insect melanogenesis. II. Inability of Manduca phenoloxidase to act on 5,6-dihydroxyindole-2-carboxylic acid. 1023 Nov 99

To study a way to covalently link arabinoxylans and proteins using a fungal laccase from the fungus Pycnoporus cinnabarinus, the effect of cysteinyl caffeic acid on the cross-linking of wheat arabinoxylans was investigated by means of capillary viscometry and RP-HPLC of alkali labile phenolic compounds. Cysteinyl caffeic acid provoked a delay in gelation and in the consumption of the esterified ferulic acid on arabinoxylans. When reacting free ferulic acid and cysteinyl caffeic acid with laccase, the ferulic acid consumption and the dehydrodimers production were also diminished. These results suggest that cysteinyl caffeic acid is oxidized while reducing the semiquinones of ferulic acid produced by laccase. Thus, ferulic acid could not be oxidized into dimers until all cysteinyl caffeic acid was consumed, preventing the cross-linking of feruloylated arabinoxylan chains. A similar mechanism is proposed in the case of caffeic acid and of L-Dopa.
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PMID:Effect of cysteinyl caffeic acid, caffeic acid, and L-dopa on the oxidative cross-linking of feruloylated arabinoxylans by a fungal laccase. 1056 23

Melanin is a recognized virulence factor in Cryptococcus neoformans; several pathogenetic mechanisms have been suggested. We studied melanin as an antifungal resistance factor. The growth of laccase-active strains of C. neoformans and C. albidus in L-DOPA resulted in the production of black pigment. The formal minimal inhibitory concentrations (MICs) of amphotericin B and fluconazole were not changed by melanization. However, when we examined those wells which contained inhibited cells, we found live cells only in wells containing melanized C. neoformans. In contrast, melanization did not protect C. albidus from killing by amphotericin B. In an amphotericin B time-kill study of C. neoformans, significantly more melanized cells than non-melanized survived for the first few hours. Fluorescence microscopy and flow cytometry analyses showed that fewer melanized cells were stained with the fluorescent dye MitoRed. Incubation of MitoRed (the model) or amphotericin B with melanin extracted from C. neoformans decreased the free concentrations of these substances. Fluconazole, in contrast, was not removed from solution by melanin. This suggests that neoformans cryptococcal melanin deposited amphotericin B in the cell wall binds, reducing its effective concentrations.
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PMID:Effects of melanin upon susceptibility of Cryptococcus to antifungals. 1280 Oct 64

A laccase (EC 1.10.3.2) was isolated from the fully browned gills of Lentinula edodes fruit bodies. The enzyme was purified to a homogeneous preparation using hydrophobic, cation-exchange and size-exclusion chromatography. SDS-PAGE analysis showed the purified laccase, Lcc 2, to be a monomeric protein of 58.0 kDa. The enzyme had an isoelectric point of around pH 6.9. The optimum pH for enzyme activity was around 3.0 against 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)diammonium salt (ABTS), and it was most active at 40 degrees C and stable up to 50 degrees C. The enzyme contained 8.6 % carbohydrate and some copper atoms. The enzyme oxidized ABTS, p-phenylenediamine, pyrogallol, guaiacol, 2,6-dimethoxyphenol, catechol and ferulic acid, but not veratryl alcohol and tyrosine. Beta-(3,4-dihydroxyphenyl)alanine (L-DOPA), which was not oxidized by a laccase previously reported from the culture filtrate of L. edodes, was also oxidized by Lcc 2, and the oxidative product of L-dopa was identified as L-DOPA quinone by HPLC analysis. Lcc 2 was able to oxidize phenolic compounds extracted from fresh gills to brown-coloured products, suggesting a role for laccase in melanin synthesis in this strain.
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PMID:Important role of fungal intracellular laccase for melanin synthesis: purification and characterization of an intracellular laccase from Lentinula edodes fruit bodies. 1294 71

Melanins, or melanin-like compounds, may play a role in the pathogenesis of a number of human fungal infections. This study investigated the production of melanin by the important opportunistic pathogen Aspergillus fumigatus. Conidia from A. fumigatus were harvested and treated with proteolytic enzymes, denaturant and hot, concentrated acid; this yielded dark particles which were similar in size and shape to the original propagules. Electron spin resonance spectroscopy revealed that the conidial-derived particles were stable free radicals consistent with an identification as melanin. Melanin particles were used to immunize BALB/c mice in order to produce a total of five anti-melanin monoclonal antibodies (mAbs). The latter mAbs were strongly reactive both with intact conidia and with extracted melanin particles by ELISA and immunofluorescence reactivity. Immunofluorescence labelling with the novel mAbs was used to examine the temporal expression of melanin during in vitro culture of A. fumigatus--melanization was confined to conidial structures and was absent from hyphae. SDS-PAGE L-3,4-dihydroxyphenylalanine (L-DOPA) substrate analysis confirmed the presence of a laccase-type activity in conidial extracts, but not in hyphae. Melanin-binding mAbs were used to detect the presence of melanized conidia in three patients with nasal aspergilloma, indicating that in vivo melanization may occur during infection.
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PMID:Production of melanin by Aspergillus fumigatus. 1497 Feb 41


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