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At least 271 records · Page 15Linked to original sources
PubMed2002

Nature of the intermediate formed in the reduction of O(2) to H(2)O at the trinuclear copper cluster active site in native laccase.

The multicopper oxidases contain at least four copper atoms and catalyze the four-electron reduction of O(2) to H(2)O at a trinuclear copper cluster. An intermediate, termed native intermediate, has been trapped by a rapid freeze-quench technique from Rhus vernicifera laccase when the fully reduced form reacts with dioxygen. This intermediate had been described as an oxygen-radical bound to the trinuclear copper cluster with one Cu site reduced. XAS, however, shows that all copper atoms are oxidized in this intermediate. A combination of EXAFS, multifrequency EPR, and VTVH MCD has been used to understand how this fully oxidized trinuclear Cu cluster relates to the fully oxidized resting form of the enzyme. It is determined that in the native intermediate all copper atoms of the cluster are bridged by the product of full O(2) reduction. In contrast, the resting form has one copper atom of the cluster (the T2 Cu) magnetically isolated from the others. The native intermediate decays to the resting oxidized form with a rate that is too slow to be in the catalytic cycle. Thus, the native intermediate appears to be the catalytically relevant fully oxidized form of the enzyme, and its role in catalysis is considered.

Binding Sites↗
PubMed2003

Alkaline transition of phytocyanins: a comparison of stellacyanin and umecyanin.

The effect of pH on Cu(I) and Cu(II) forms of the isolated soluble domain of the stellacyanin from Rhus vernicifera (SCu), the Japanese lacquer tree, has been studied by electronic and NMR spectroscopy and using direct electrochemical measurements. A pK(a) value of 10.1-10.4 is observed for the alkaline transition in this oxidized phytocyanin and results in a slightly altered active-site structure, as indicated by changes in the visible and paramagnetic (1)H NMR spectra. Electrochemical studies show that the pK(a) value for this transition in SCu(I) (reduced SCu) is 11.0. These results are compared with those recently obtained for other phytocyanins, and in particular umecyanin. In all cases, the alkaline transition is caused by the deprotonation of the surface lysine residue adjacent to the axial ligand. This lysine residue is completely conserved in known phytocyanin sequences. Also highlighted in these studies are the remarkable active-site similarities between stellacyanin and umecyanin.

Amino Acid Sequence↗
PubMed2003

Antioxidant activities of rosemary, sage, and sumac extracts and their combinations on stability of natural peanut oil.

The antioxidant efficacy of rosemary (Rosmarinus officinalis L.), sage (Salvia fruticosa L.), and sumac (Rhus coriaria L.) extracts and combinations at 4% concentrations (wt/vol, extract/oil) were investigated. Methanolic extracts of rosemary, sage, sumac, and their combinations were applied to peanut oil stored at 80 degrees C for 24 h. The antioxidant effect was determined by measuring the peroxide value. All extracts showed antioxidant effects compared with control. But the antioxidant effect of all extracts was low compared with that of butylated hydroxytoluene. Rosemary extract (except for 3 and 4 h) exhibited the most antioxidant effect compared with other individual extracts. Of blends, the most effective ones were sage plus sumac combinations. Sumac extract is also promising as a source of natural antioxidants.

Antioxidants↗
PubMed2003

[Study on gallnuts development and its tannin amount].

OBJECTIVE: To find out the suitable time for collecting gallnuts. When Kaburgaia rhusicola parasailed on leaflets of Rhus potainii, the parts of the leaflets developed into gallnuts. METHOD: The regulation of development and tannin amount during whole growing stage were studied. RESULT: K. rhusicola lived in gallnuts for about 80 days. The gallnuts developed quickly during earlier stage and slowly during later stage. Gallnuts maturated from 12th, July to 30th, July, which had no relations with the size and the time for forming, but had relations with development at earlier stage. It developed quickly with earlier maturation and developed slowly with later maturation. Its tannin amount kept stable during the whole growing stage. CONCLUSION: The best harvesting days are those shortly after 7th, July.

Animals↗
PubMed1999

Intake, digestibility, and passage of a commercially designed diet by two Propithecus species.

The digestibility and passage of an experimental diet was used to compare the digestive physiology of two Propithecus species: P. verreauxi and P. tattersalli. Though both animals have a similar feeding ecology, the captive status of P. verreauxi is considered more stable than that of P. tattersalli. The test diet included a local tree species, Rhus copallina, at 15% of dry matter intake (DMI) and Mazuri Leafeater Primate Diet at 85% of DMI. The chemical composition of the diet (dry matter basis) was 25% crude protein, 34% neutral detergent fiber (NDF), and 22% acid detergent fiber (ADF) with a gross energy of 4.52 kcal/g. After a 6 week acclimation to the experimental diet, animals were placed in research caging. After a 7 day adjustment period, animals were dosed with chromium mordant and Co-EDTA as markers for digesta passage and all feed refusals and feces were collected at timed intervals for 7 days. Digestibility values, similar for both species, were approximately 65% for dry matter, crude protein, and energy, and 40% and 35% respectively, for NDF and ADF. Transit times (17-18.5 hr) and mean retention times (31-34 hr) were not significantly different between species, and there was no difference between the chromium mordant and Co-EDTA. Serum values for glucose, urea, and non-esterified fatty acids (NEFA) were obtained during four different time periods to monitor nutritional status. While there was no change in serum glucose, serum urea increased over time. The NEFAs increased across all four time periods for P. verreauxi and increased for the first three periods then decreased in the last period for P. tattersalli. Results obtained indicate no difference in digestibility nor digesta passage between species, and that both Propithecus species were similar to other post-gastric folivores.

Animal Feed↗
PubMedDate not supplied

Electrophoretic analysis of coniferyl alcohol oxidase and related laccases.

Gradient gel electrophoretic methods enabled a distinction to be made between coniferyl alcohol oxidase (CAO) of lignifying cell walls and a pI approximately 9 pine "laccase" recently implicated in lignification (Science 1993 260, 672). Following treatment of a partially purified protein mixture from developing xylem of Pinus strobus with 2-[N-morpholine]ethanesulfonic acid (MES) buffer, isoelectric focusing and sodium dodecyl sulphate-polyacrylamide gel electrophoresis indicated that CAO had been selectively precipitated by MES and thereby purified to electrophoretic homogeneity. Purified CAO was determined to be a cell-wall-bound glycoprotein (38% glycan), M(r) 107,500, pI 7.6, pH and temperature optima 6.3 and 30 degrees C, respectively. By graphite-furnace atomic-absorption analysis, CAO contained one copper atom per protein molecule. Proteins obtained from lignifying cambial derivatives of conifers (family Pinaceae) and from Rhus typhina bark were compared with CAO and the pI approximately 9 pine "laccase" following electrophoresis and Western blotting. For Abies balsamea, Larix laricina, Picea rubens, Pinus banksiana, Pinus taeda, and R. typhina, the isoelectric points of oxidatively active bands were identical to those of purified CAO. In addition, for all species only the pI 7.6 band was immunoreactive with antibodies against periodate-deglycosylated CAO.

Alcohol Oxidoreductases↗
PubMed1996

Cloning, expression, and spectroscopic characterization of Cucumis sativus stellacyanin in its nonglycosylated form.

The cDNA encoding the 182 amino acid long precursor stellacyanin from Cucumis sativus was isolated and characterized. The protein precursor consists of four sequence domains: I, a 23 amino acid hydrophobic N-terminal signal peptide with features characteristic of secretory proteins; II, a 109 amino acid copper-binding domain; III, a 26 amino acid hydroxyproline- and serine-rich peptide characteristic of motifs found in the extension family, extracellular structural glycoproteins found in plant cell walls; and IV, a 22 amino acid hydrophobic extension. Maturation of the protein involves posttranslational processing of domains I and IV. The copper-binding domain (domain II), which shares high sequence identity with other stellacyanins, has been expressed without its carbohydrate attachment sites, refolded from the Escherichia coli inclusion bodies, purified, and characterized by electronic absorption, EPR, ESEEM, and RR spectroscopy. Its spectroscopic properties are nearly identical to those of stellacyanin from the Japanese lacquer tree Rhus vernicifera, the most extensively studied and best characterized stellacyanin, indicating that this domain folds correctly, even in the absence of its carbohydrate moiety. The presence of a hydroxyproline- and serine-rich domain III suggests that stellacyanin may have a function other than that of a diffusible electron transfer protein, conceivably participating in redox reactions localized at the plant cell wall, which are known to occur in response to wounding or infection of the plant.

Amino Acid Sequence↗
PubMed1994

EPR studies of ligand binding to the type 2/type 3 cluster in tree laccase.

Detailed investigations of the EPR-active copper ion in the trinuclear type 2/type 3 cluster site of T1Hg Rhus vernicifera laccase suggest that at least some inhibitor anions bind to what was an EPR-silent copper center of the resting enzyme. The key observation is that with [15N]azide the adduct exhibits remarkably well resolved ligand hyperfine structure indicative of splitting from three protein (histidine) nitrogens and one azide nitrogen. This accords nicely with recent X-ray diffraction studies of adducts of the related enzyme, ascorbate oxidase (A. Messerschmidt, H. Luecke, and R. Huber, 1993, J. Mol. Biol. 230, 997-1014). We have also characterized a previously unknown dicyanide adduct that exhibits an EPR signal with ligand hyperfine structure from two protein nitrogens and two cyanide carbons. Cyanide may bind to the same copper center as azide, but not without a structural reorganization of the cluster. The results also imply that the protonation of a bridging ligand within the type 2/type 3 cluster explains the pH dependence of anion binding. Imidazole interacts with the protein but does not bind to the EPR-active copper. In keeping with the function of the dioxygen reduction site, the type 2/type 3 cluster in laccase proves to be an extremely flexible host capable of accommodating a variety of ligands.

Azides↗
PubMed1998

Recent advances in the discovery and development of flavonoids and their analogues as antitumor and anti-HIV agents.

Antitumor and anti-HIV flavonoids and their analogues will be reviewed with emphasis on those discovered in our laboratory. The active antitumor compounds include the antileukemic tricin (1) and kaempferol-3-O-beta-D-glucopyranoside (2) from Wikstroemia indica, the cytotoxic hinokiflavone (3) from Rhus succedanea, the cytotoxic isoflavone (8) from Amorpha fruticosa, two dihydroxypentamethoxyflavones (9, 10) from Polanisia dodencandra. The development of synthetic 2-phenyl-4-quinolones as potent cytotoxic antimitotic flavonoid analogues and 2-phenylthiochromen-4-ones as potent antitumor flavonoid analogues will be presented. Selected results from other laboratories and antitumor-related biological studies also will be discussed. Flavonoids have also been investigated as potential anti-HIV agents. In our laboratory, acacetin-7-O-beta-D-galactopyranoside (131) from Chrysanthemum morifolium and chrysin (102), as well as apigenin-7-O-beta-D-glucopyranoside (130), from Kummerowia striata, have been found to exhibit anti-HIV activity. In other studies, some flavonoids and related compounds have been investigated as inhibitors of HIV-1 reverse transcriptase, protease, and integrase. The isolation and structural modification of such plant-derived active principles provide a continuing source of potential antitumor and anti-HIV agents.

Animals↗
PubMed2004

Dual inhibition of 5-lipoxygenase/cyclooxygenase by a reconstituted homeopathic remedy; possible explanation for clinical efficacy and favourable gastrointestinal tolerability.

OBJECTIVE: In order to elucidate potential anti-inflammatory activities of Zeel comp. N and its constituents, the inhibition of the synthesis of Leukotriene B4 (LTB4) and Prostaglandin (PGE2) by 5-lipoxygenase (5-LOX) and cyclo-oxygenase 1 and 2 (COX 1 and 2) respectively were examined in vitro. MATERIALS: Human HL-60 cells, differentiated for 6-8 days with DMSO (1.2% v/v) were used for the 5-LOX assay. The COX activity assays were carried out with purified enzymes, COX 1 (ram seminal vesicles), COX 2 (sheep placenta) and with human THP-1 cells, differentiated for 24 h with PMA (50 nM). METHODS: LTB4 and PGE2 production in the 5-LOX and COX assays respectively were determined by enzyme linked immunoassays. RESULTS: A reconstituted Zeel comp. N combination as well as its constituent mother tinctures of Arnica montana, Sanguinaria canadensis and Rhus toxicodendron (Toxicodendron quercifolium) showed distinct inhibitory effects on the production of LTB4 by 5-LOX (IC50 values of 10, 20, 2 and 5 microg/ml respectively) and on the synthesis of PGE2 by COX 1 (IC50 values of 50, 80, 40 and 20 microg/ml respectively) and COX 2 enzymes (IC50 values of 60, 110, 50 and 20 microg/ml respectively). The mother tincture of Solanum dulcamara inhibited the production of PGE2 by COX 1 (IC50 40 microg/ml) and COX 2 (IC50 150 microg/ml) but not production of leukotriene LTB4 by 5-LOX. CONCLUSIONS: The observed dual inhibition of both LOX- and COX-metabolic pathways may offer an explanation for the reported clinical efficacy and the favorable gastrointestinal tolerability of the original remedy Zeel comp. N.

Cyclooxygenase Inhibitors↗
PubMed2001

Modification of lignin for the production of new compounded materials.

The cell walls of woody plants are compounded materials made by in situ polymerization of a polyphenolic matrix (lignin) into a web of fibers (cellulose), a process that is catalysed by polyphenoloxidases (laccases) or peroxidases. The first attempt to transform the basic strategy of this natural process for use in human craftsmanship was the ancient lacquer method. The sap of the lacquer tree (Rhus verniciflua) contains large amounts of a phenol (urushiol), a polysaccharide and the enzyme laccase. This oil-in-water emulsion solidifies in the presence of oxygen. The Chinese began using this phenomenon for the production of highly creative artwork more than 6,000 years ago. It was the first example of an isolated enzyme being used as a catalyst to create an artificial plastic compound. In order to apply this process to the production of products on an industrial scale, an inexpensive phenol must be used, which is transferred by an enzyme to active radicals that react with different components to form a compounded material. At present, the following approaches have been studied: (1) In situ polymerization of lignin for the production of particle boards. Adhesive cure is based on the oxidative polymerization of lignin using phenoloxidases (laccase) as radical donors. This lignin-based bio-adhesive can be applied under conventional pressing conditions. The resulting particle boards meet German performance standards. By this process, 80% of the petrochemical binders in the wood-composite industry can be replaced by materials from renewable resources. (2) Enzymatic copolymerization of lignin and alkenes. In the presence of organic hydroperoxides, laccase catalyses the reaction between lignin and olefins. Detailed studies on the reaction between lignin and acrylate monomers showed that chemo-enzymatic copolymerization offers the possibility to produce defined lignin-acrylate copolymers. The system allows control of the molecular weights of the products in a way that has not been possible with chemical catalysts. This is a novel attempt to enzymatically induce grafting of polymeric side chains onto the lignin backbone, and it enables the utilization of lignin as part of new engineering materials. (3) Enzymatic activation of the middle-lamella lignin of wood fibers for the production of wood composites. The incubation of wood fibers with a phenol oxidizing enzyme results in oxidative activation of the lignin crust on the fiber surface. When such fibers are pressed together, boards are obtained which meet the German standards for medium-density fiber boards (MDF). The fibers are bound together in a way that comes close to that by which wood fibers are bound together in naturally grown wood. This process will, for the first time, yield wood composites that are produced solely from naturally grown products without any addition of resins.

Biopolymers↗
PubMed1983

Reduction of laccase type 1 copper by 3,4-dihydroxyphenylalanine and other catechol derivatives.

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.

Catechols↗
PubMed1990

Inhibition of protease activities of periodontopathic bacteria by extracts of plants used in Kenya as chewing sticks (mswaki).

Extracts from five plants used as chewing sticks, and tannic acid, gallic acid and methyl ester of gallic acid, were tested for their ability to inhibit proteolytic activities of three strains of Bacteroides gingivalis, three strains of Bacteroides intermedius and two strains of Treponema denticola. Aqueous extract from the plants Rhus natalensis and Euclea divinorum were the most inhibitory of those tested, inhibiting by 50% the proteolytic activity of the test organisms, at concentrations of up to 200 micrograms/ml. Tannic and gallic acids had similar effects at concentrations of less than 10 micrograms/ml, while the methyl ester of gallic acid was less inhibitory. These findings suggest that extracts from plants used as chewing sticks may possess enough inhibitory components to interfere with the virulence and growth of periodontopathic bacteria in vivo, provided they are able to gain access to the subgingival sites such bacteria preferentially inhabit.

Bacteroides↗
PubMed1978

Magnetic susceptibility of laccases and ceruloplasmin.

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.

Catechol Oxidase↗
PubMed1979

Substituent effects on the electron transfer reactivity of hydroquinones with laccase blue copper.

Stopped-flow kinetic studies of the anaerobic reduction of Rhus vernicifera laccase (monophenol, dihydroxyphenylalanine:oxygen oxidoreductase, EC 1.14.18.1) type 1 copper by 25 mono- and disubstituted hydroquinones (H2Q-X) have been performed at 25 degrees C and pH 7.0 in 0.5 M phosphate. All of the data are compatible with a mechanism involving rapid enzyme-substrate complex formation followed by rate-limiting intra-complex electron transfer. ES complex formation constants (Qp) for many substrates are strikingly insensitive to the electronic characteristics of the substituent X, falling within the range 5--50 M-1. It is shown that this result may be accounted for if only the singly ionized forms of the substituted hydroquinones are bound by the enzyme. All of the substrates exhibiting exceptionally high Qp values (greater than 50 M-1) have X groups capable of functioning as ligands; substituents with lone pairs of electrons may facilitate enzyme-substrate complex formation by enabling hydroquinone to function as a bidentate bridging ligand between the type 2 and type 3 copper sites. Intra-complex electron transfer rate constants for most substrates are remarkably insensitive to the thermodynamic driving force for the oxidation of H2Q-X to the corresponding semiquinone, the average value for ten substrates being 30 +/- 10 s-1. The electron transfer reactivity of polyphenols with laccase blue copper therefore appears to be controlled largely by protein-dependent activation requirements rather than by the oxidizability of the substrate.

Binding Sites↗
PubMed1988

Three-dimensional model of stellacyanin and its implications for electron transfer reactivity.

Experimental data were combined with computational methods in constructing a hypothetical three-dimensional model for the blue single copper protein Rhus stellacyanin (St). The known sequence of stellacyanin and its homology with plastocyanin (Pc) were used together with the results of spectroscopic studies of the protein that yielded the current assignment of two histidines, one cysteine and a disulfide sulfur as copper ligands in stellacyanin. By computer graphics and energy minimization the folding of the protein was predicted. The model structure is somewhat less regular than Pc as judged by surface area and energy comparisons, but it is a stable structure. Besides rotation of one imidazole ring the copper site undergoes no change even in the absence of the copper ion and the model shows that the site can be constructed with the four assumed copper ligands without forming a strained system. The structure also indicates that a carbonyl oxygen atom is near the copper, thus the site may have analogy to the Alcaligenes denitrificans azurin (Az) site, although the amino acid sequence is more homologous to that of Pc. The model indicates that aspartate 49, reductively labeled by Cr(III), is near the copper center and homologous to the site labeled by Cr(III) on Pc. Also homologous to Pc is a tyrosine residue adjacent to the aspartate. This tyrosine has been implicated in Pc electron transfer and thus is probably involved in electron transfer reactivity of St as well. The higher reactivity of St with small-molecule redox reagents compared to Az and Pc, may be due to the proximity of the above-mentioned aspartate 49 to the Cu, or the greater exposure of one of the Cu cysteine ligands, in the predicted structure as compared to that in the known Pc and Az structures.

Amino Acid Sequence↗
PubMed1991

Three-dimensional model for stellacyanin, a "blue" copper-protein.

A three-dimensional model of the "blue" copper-glycoprotein stellacyanin from Rhus vernicifera has been derived by computer graphics, energy minimization and molecular dynamics techniques. The initial atomic co-ordinates were obtained by making substitutions and insertions in the known structure of another blue copper-protein, cucumber basic protein (CBP), which is 46% homologous with stellacyanin and has similar spectroscopic properties. An important difference between CBP and stellacyanin is that the latter lacks methionine, a residue that forms an exceptionally long bond to the copper atom in all blue copper-proteins of known structure. In the aligned amino acid sequences, stellacyanin has glutamine 97 at the position that corresponds to the copper-binding methionine 89 in CBP. The hypothesis that the copper atom in stellacyanin is co-ordinated by the side-chain functional groups of histidine 46, cysteine 87, histidine 92 and glutamine 97 leads to a model that enables the spectroscopic properties, redox potential and electron-transfer kinetics of the protein to be rationalized. The present model for stellacyanin is more plausible than an antecedent model derived from the structure of plastocyanin. This demonstrates that the output from molecular modeling calculations is strongly dependent on the input, and that sequence homology with the target molecule is an important criterion for the selection of a starting model.

Amino Acid Sequence↗