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PubMed1983

Quantitative Cu(I) determination using X-ray absorption edge spectroscopy: oxidation of the reduced binuclear copper site in type 2 depleted Rhus laccase.

We report a procedure, through difference comparison of X-ray absorption edge spectra, for the quantitative determination of Cu(I) content in copper complexes of mixed oxidation state composition. This technique is tested on copper model systems and then used to quantitatively determine that untreated T2D Rhus laccase contains 70 +/- 15% Cu(I). Whereas excess ferricyanide is demonstrated not to alter the Cu(I) content of the untreated T2D, aqueous peroxide and nitrite at pH 6.0 are shown to oxidize the cuprous type 3 site and generate met T2D protein forms.

Binding Sites↗
PubMed1983

EXAFS investigation of the binuclear cupric site in met T2D Rhus laccase and its azide bound derivative.

EXAFS analysis of met T2D Rhus laccase and its azide bound derivative indicates an average of 0.33 S at 2.09 A and 3-4 N (or O) atoms at 2.00 A per copper atom for the three copper centers. Using the plastocyanin Cu(II) EXAFS spectrum to model the type 1 site in laccase, a difference EXAFS spectrum for the type 3 site is generated; this spectrum enables assignment of the one S ligand in met T2D to the type 1 site and indicates no evidence of a detectable copper scatterer for the coupled binuclear copper site. Implications regarding type 3 optical features and related studies on the hemocyanins are also discussed.

Azides↗
PubMed1992

The removal of the type-2 copper from Rhus vernicifera laccase.

We have studied the removal of the type-2 copper from tree laccase (Rhus vernicifera) by treatment with EDTA at pH 5.2 in the presence of a redox buffer containing ferri- and ferrocyanide. The efficiency with which the copper is removed depends on the Fe(CN) 6(4-)/Fe(CN) 6(3-) ratio. We have varied this ratio from approx. 2:1 to about 50:1 and the best results were obtained with the highest ratio, i.e., the most cathodic solution potential. Nevertheless, the presence of Fe(CN) 6(3-) is required for the procedure to be effective. Although we cannot exclude the possibility that a mixed-valence form of laccase is the reactive species, we believe the results are better explained by a model which assumes that the removal of the type-2 copper depends upon an ordered sequence of oxidation-reduction reactions. Specifically, we propose that the copper is released as the monovalent ion from previously reduced laccase and then reoxidized in solution and sequestered with EDTA. The reoxidation step drives the reaction because recombination with the protein is inhibited when copper is in the divalent form. In testing this model, we have also shown that the type-2 copper can be removed under strictly reducing conditions when 4,4'-dicarboxy-2,2'-biquinoline (BCA) is present to complex the copper(I) ion. Although the BCA method is effective, the reaction takes longer, perhaps because of the limited solubility of BCA at the pH values of interest. Finally, we have found that the best results are obtained with either method when a cyanometalate ion such as Fe(CN) 6(3-) or Co(CN) 6(3-) is present in the medium. The exact role of this factor has yet to be established, but there is no indication that free cyanide has a role in the process. The most likely interpretation is that some type of binding interaction with the protein facilitates copper release.

Buffers↗
PubMed1990

Drug-induced, photosensitive, erythema multiforme-like eruption: possible role for cell adhesion molecules in a flare induced by Rhus dermatitis.

Drug-induced, photosensitive erythema multiforme has not been reported, although drugs and sunlight are listed among precipitating factors in erythema multiforme. We describe a case of a drug-induced erythema multiforme-like eruption in a photodistribution that was reproduced by clinical challenge with the drug and sunlight. On contact with Rhus verniciflua, the Japanese lacquer tree, the patient had a flare of the eruption, which was limited to the areas previously exposed to sun. Immunohistochemical studies suggested that the keratinocytes in the skin that retain teh photoactivated substances may facilitate epidermal invasion of lymphocytes by persistent expression of intercellular adhesion molecule-1.

Adult↗
PubMed1984

On the spectral features associated with peroxide reactivity of the coupled binuclear copper active site in type 2 depleted and native Rhus laccase.

We report herein an X-ray absorption spectroscopic (XAS) determination of the oxidation state of the copper sites in T2D and native Rhus laccase. The increase in intensity of the 330 nm absorption feature which results from peroxide titration of T2D laccase (T3: [Cu(I)Cu(I)], T1: [Cu(II)]) is found to correlate linearly with the percent of oxidation of the binuclear copper site (determined by XAS analysis). This indicates that peroxide oxidizes but does not bind to the T3 site. We have used this correlation to determine that native laccase, as isolated, contains approximately 25% reduced T3 sites and that all spectral changes observed upon peroxide addition to native laccase can be accounted for by oxidation of these reduced sites. The importance of this result to previous reports of peroxide binding at the laccase active site is discussed.

Binding Sites↗
PubMed2000

A bichalcone from the twigs of Rhus pyroides.

The twigs of Rhus pyroides yielded a novel bichalcone 2',4",2"'-trihydroxy-4',4"'-dimethoxy-4-O-5"'-bichalcone. It was identified on the basis of spectroscopic data including 1D and 2D NMR spectroscopy. The name rhuschalcone-1 is proposed.

Chalcone↗
PubMed1979

Electron transfer kinetics between Rhus vernicifera stellacyanin and cytochrome c (horse heart cytochrome c and Pseudomonas cytochrome c551).

The electron transfer reactions between Rhus vernicifera stellacyanin and either horse heart cytochrome c or Pseudomonas aeruginosa cytochrome c551 were investigated by rapid reaction techniques. The time course of electron transfer is monophasic under all conditions, and thus consistent with a simple formulation of the reaction. Both stopped-flow and temperature-jump experiments yield equilibrium constants in reasonable agreement with values calculated from the redox potentials. The differences in reaction rate between the two cytochromes and stellacyanin are discussed in terms of the Marcus theory.

Animals↗
PubMed1979

Spectroscopic and catalytic properties of Rhus vernicifera laccase depleted in type 2 copper.

1. The type 2 copper in Rhus vernicifera laccase was completely removed without loss of other types of copper. The properties of this protein derivative and the role of type 2 copper in the catalytic action of laccase was investigated. 2. The molar extinction coefficient at 614 nm of the blue chromophore decreases from 5700 to 4700 cm-1 on removal of type 2 copper. There are no apparent absorption changes at other wavelengths in the visible or near ultraviolet region when this copper is taken away. The electron-paramagnetic-resonance (epr) parameter A parallel and the linewidth of type 1 Cu2+ decreases on removal of type 2 copper. 3. The rate of reduction of type 1 Cu2+ is not affected by removal of type 2 copper but the reduction of the two-electron acceptor is greatly impaired. These results strongly support the idea that type 1 Cu2+ is the primary site for electron transfer between substrate and enzyme and that the two-electron acceptor in the native enzyme is reduced by simultaneous electron transfer from reduced types 1 and 2 copper. 4. Reoxidation of types 1 and 3 copper and the formation of the oxygen intermediate are the same processes in native and type-2-depleted enzyme. These observations suggests that type 2 copper is not involved in the formation and rapid decay of the oxygen intermediate and that it is not necessary for the stabilization of this intermediate. 5. Two new epr signals are observed on reoxidation of reduced type-2-depleted laccase. One is temporarily formed on re-reduction of reoxidized enzyme and it is suggested that it might arise from copper, possibly type 3 copper. The other one is stable for hours and it is proposed that it might come from a modified oxygen intermediate.

Anaerobiosis↗
PubMed2000

Assay for Laccase activity by microcalorimetry: laccase was extracted from china lacquer of Rhus vernicifera.

The reactions between Laccase (extracted from China lacquer of Rhus vernicifera) and various substrates (3,4-Dihydroxybenzaldehyde, Guaiacol, Pyrogallol, Gallic acid) have been studied using LKB-2107 batch microcalorimetry system. Based on calorimetry, a new method has been proposed. Laccase activity and the Michaelis constant K(m) have been determined simultaneously by this method. The method is simple, sample-saving, and valid for a wider range of substrate concentrations. Furthermore, it can be extended for assaying other enzymes catalyzing reactions using this method.

Calorimetry↗
PubMed1998

Suppression of recurrent genital herpes simplex virus type 2 infection by Rhus javanica in guinea pigs.

Rhus javanica has been shown to exhibit anti-herpes simplex virus (HSV) activity and potentiate the anti-HSV activity of acyclovir in vitro and in vivo. This extract was examined for its suppressive efficacy on recurrent genital infection in guinea pigs. Guinea pigs were primarily infected intravaginally with HSV type 2 (HSV-2). Prophylactic oral administration, at the dose corresponding to human use, of R. javanica significantly reduced the incidence, severity and/or frequency of spontaneous and severe skin lesions as compared with latently infected guinea pigs administered with water. This prophylactic efficacy was confirmed by the crossover administration, for more than 2 months, of R. javanica and water to the infected guinea pigs. Toxicity, such as weight loss, from R. javanica administration was not observed in the guinea pigs. When recurrent HSV-2 disease was induced by ultraviolet irradiation 3 months after primary infection, the prophylaxis with R. javanica was also significantly effective in reducing the severity of ultraviolet-induced skin lesions. Thus, prophylaxis of recurrent genital HSV-2 infection with R. javanica may preserve the efficacy of acyclovir by reducing both the use of acyclovir and the appearance of acyclovir-resistant viruses.

Administration, Intravaginal↗
PubMed2001

Antioxidant activity of a Rhus verniciflua Stokes ethanol extract.

A fractionated ethanol extract derived from Rhus Verniciflua Stokes (RVS) was assessed in both organic and aqueous media for the purpose of characterizing the mechanisms of antioxidant activity. RVS, an indigenous plant to Korea, was initially extracted with ethanol and characterized to contain a 90 KDa-ABTS reactive protein possessing 0.662 ng/mg copper. This characterization suggested that a primary component of RVS was Laccase, an oxidase enzyme complex. RVS exhibited a significant (P < 0.01) concentration-dependent inhibition of linoleic acid oxidation in an emulsion system up to 48 hours of incubation. Free radical scavenging activity of both a stable radical (e.g DPPH) and hydroxyl (e.g. *OH) radical followed a concentration-dependent pattern in different model systems. Using a liposome model with peroxyl radicals generated by AAPH, a significant extension of both the lag phase and a reduction of peak propagation of peroxyl radicals by RVS over a concentration range of 1 to 10 microg/ml was observed. RVS ethanol extract was also found to protect human low-density lipoprotein (LDL) from oxidative modification, mediated by cupric ion at 37 degrees C. Finally, RVS was found to be effective at protecting against plasmid DNA strand breakage induced by peroxyl free radicals in an aqueous medium. Our findings show that the ethanol fraction derived from RVS contained significant antioxidant activity in both polar and non-polar mediums.

Antioxidants↗
PubMed1984

X-ray absorption study of Rhus laccase: evidence for a copper-copper interaction, which disappears on type 2 copper removal.

X-ray absorption spectra are reported for the multi-Cu oxidase Rhus vernicifera laccase in oxidized and fully reduced forms and for laccase from which the type 2 Cu has been depleted (T2D). The structure of the Cu K edge for both preparations shows the presence of CuII and CuI in the oxidized and reduced states, respectively. As previously reported by LuBien et al. (1981), removal of the type 2 Cu leads to reduction of the type 3 center, which can be reoxidized with H2O2. Fourier transforms of the extended X-ray absorption fine structure (EXAFS) give well-defined first and outer shell scattering peaks. Analysis of the first shell peak is complicated by the heterogeneity of the Cu sites. When (imidazole)4CuIISO4 is used as a model of the average Cu-ligand interactions, it is shown that all of the first shell peaks contain 2.7-3.5 near neighbors per Cu, at an average distance of 1.97-1.98 A. For T2D laccase, the fit is improved by inclusion of one-third of a sulfur atom at 2.19 A, corresponding to the presumptive cysteine ligand of the type 1 Cu, which remains in the preparation containing three Cu atoms per molecule. The outer shell region shows two peaks characteristic of scattering from distant imidazole atoms. For T2D laccase the filtered outer shell contribution can be satisfactorily fit by scattering from an average of 2.1-2.4 imidazole groups. For native laccase, however, imidazole alone cannot satisfactorily model the outer shell contribution.(ABSTRACT TRUNCATED AT 250 WORDS)

Copper↗
PubMed1977

Pulsed electron paramagnetic resonance studies of types I and II coper of Rhus vernicifera laccase and porcine ceruloplasmin.

Electron spin-echo decay envelopes for types I and II copper of Rhus vernicifera laccase and for type II copper of procine ceruloplasmin have been studied. Nuclear modulation patterns show that imidazole is a ligand for all of them. The linear electric field effect (LEFE) in EPR was studied for type I copper in a laccase preparation from which type II had been removed. The symmetry of the site is near tetrahedral and the magnitude of the LEFE is correlated with the intensity of blue color.

Animals↗
PubMed1997

Alkaline transition of Rhus vernicifera stellacyanin, an unusual blue copper protein.

Stellacyanin from Rhus vernificera is a blue copper protein in which the metal is coordinated to a Cys, two His, and a Gln residue. It displays a low redox potential, a fast electron exchange rate, and a reversible alkaline transition. We have studied this transition in Cu(II)- and Co(II)-stellacyanin by means of electronic and NMR spectroscopy. The data indicate that a conformational rearrangement of the metal site occurs at high pH. A drastic alteration in the Gln coordination mode, as initially proposed, is discarded. These results show that the metal site in stellacyanin is more flexible than the sites of other blue copper proteins. The present study demonstrates that the paramagnetic shifts of the bound Cys in the Co(II) derivative are sensitive indicators of the electron delocalization and conformational changes experienced by this residue.

Azurin↗
PubMed1997

In vitro anti-HIV activity of biflavonoids isolated from Rhus succedanea and Garcinia multiflora.

Eleven biflavonoids, including amentoflavone (1), agathisflavone (2), robustaflavone (3), hinokiflavone (4), volkensiflavone (5), morelloflavone (7), rhusflavanone (9), succedaneaflavanone (10), GB-1a (11), GB-1a 7"-O-beta-glucoside (13), and GB-2a (14) isolated from Rhus succedanea and Garcinia multiflora, as well as their methyl ethers, volkensiflavone hexamethyl ether (6), morelloflavone heptamethyl ether (8), and GB-1a hexamethyl ether (12), were evaluated for their anti-HIV-1 RT activity. The results indicated that compounds 3 and 4 demonstrated similar activity against HIV-1 reverse transcriptase (RT), with IC50 values of 65 microM. Compounds 1, 2, 7, 11, and 14 were moderately active against HIV-1 RT, with IC50 values of 119 microM, 100 microM, 116 microM, 236 microM, and 170 microM, respectively. Morelloflavone (7) also demonstrated significant antiviral activity against HIV-1 (strain LAV-1) in phytohemagglutinin-stimulated primary human peripheral blood mononuclear cells at an EC50 value of 6.9 microM and a selectivity index value of approximately 10. The other biflavonoids were either weakly active, inactive, or not selective against HIV-1 in human lymphocytes.

Anti-HIV Agents↗
PubMed1980

Optical properties of japanese-lacquer-tree (Rhus vernicifera) laccase depleted of type 2 copper(II). Involvement of type-2 copper(II) in the 330nm chromophore.

1. Spectroscopic and functional properties of Japanese-lacquer-tree (Rhus vernicifera) laccase were re-investigated, with special emphasis on the relationships between the different types of copper centres (Types 1, 2, and 3). 2. On removal of the Type 2 Cu(II), a decrease of absorbance occurred in the wavelength region above 650 nm (delta epsilon 750 = 300 M-1 . cm-1) and around 330 nm (delta episom 330 up to 2200 M-1 . cm-1). 3. Reductive titrations with ascorbic acid or ferrocyanide showed that the electron-accepting capacity of the partial apoprotein is one electron-equivalent lower than that of the native protein, i.e. the protein two-electron acceptor is present in the oxidized state in spite of absorbance loss at 330 nm. 4. The 330 nm chromophore apparently depends on the presence of both the Type 2 and the Type 3 copper in the oxidized state. 5. This finding may have implications in the relative location of Type 2 and 3 copper centres and on the redox behaviour of laccase.

Circular Dichroism↗
PubMed1980

Titrations with ferrocyanide of japanese-lacquer-tree (Rhus vernicifera) laccase and of the type 2 copper-depleted enzyme. Interrelation of the copper sites.

1. Redox titrations are reported of the metal centres in Japanese-lacquer-tree (Rhus vernicifera) laccase with ferrocyanide. 2. The redox potential of Type 1 Cu was found to increase with ferrocyanide concentration up to a limiting value similar to that for the Type 1 Cu in Type 2 Cu-depleted enzyme (which is independent of ferrocyanide concentration). 3. The redox potential of the two-electron acceptor (Type 3 Cu) is also independent of ferrocyanide concentration in Type 2 Cu-depleted enzyme and lower than values reported for the native enzyme. 4. The two-electron acceptor is present in the oxidized state in the Type 2 Cu-depleted enzyme, though the latter lacks the 330 nm absorption band. 5. The redox potential of Type 2 Cu also depends on ferrocyanide concentration, at least in the presence of azide. 6. The redox potentials are affected by freezing the solutions and/or addition of azide, the latter binding to Type 2 Cu with affinity dependent on the redox state of the two-electron acceptor.

Binding Sites↗
PubMed1981

Dependence on freezing of the geometry and redox potential of type 1 and type 2 copper sites of Japanese-lacquer-tree (Rhus vernicifera) laccase.

The room-temperature e.p.r. spectrum of the Japanese-lacquer-tree (Rhus vernicifera) laccase shows A parallel (the hyperfine splitting constant) and g parallel values of both the Type 1 and Type 2 Cu appreciably different from those measured at liquid-N2 temperature. The geometry of the sites, as inferred from the room-temperature e.p.r. parameters, is more consistent with their redox properties. A rough correlation is found between A parallel and g parallel values and redox potential of the blue copper in several enzymes.

Chemical Phenomena↗