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At least 163 records · Page 9Linked to original sources
PubMed1983

Nitrite reactivity of the binuclear copper site in T2D Rhus laccase: preparation of half met-NO2- T2D laccase and its correlation to half met-NO2- hemocyanin and tyrosinase.

Through chemistry directly comparable to that of the hemocyanins and tyrosinase, half met-NO2- T2D laccase derivatives have been prepared; this NO2- reactivity entails both two electron oxidation of the cuprous binuclear site in deoxy T2D laccase and one electron reduction of the coupled cupric site in the met derivative. However, the labile ligand substitution chemistry and lack of dimer formation in half met-NO2- T2D are in marked contrast to behavior of the simpler binuclear copper containing proteins under analagous conditions. This chemistry supports and extends our earlier studies on the ferrocyanide-generated half met T2D which first indicated an inability of exogenous ligands to bridge the binuclear copper site in laccase.

Binding Sites↗
PubMed1990

New method for removing type 2 copper from Rhus laccase.

A new procedure is described for preparing tree laccase that is missing the type 2 copper. The derivative has only about 5% of the activity of the native enzyme, and some, or all, of the residual activity could be due to traces of holoprotein. The type 1 copper is fully oxidized in the purified type-2-depleted protein, while the type 3 site is reduced to the extent of at least 85%. However, the type 3 coppers can be reoxidized by treatment with excess H2O2. Reconstitution is achieved by incubation with Cu(I), and the remetalated protein exhibits the activity and the spectral properties of the native enzyme. The type 2 copper is removed by dialysis against a redox buffer containing ferri- and ferrocyanide ions as well as EDTA. More than 25% of the total copper is removed from laccase during the procedure, but the type-2-depleted fraction is readily isolated by means of an ion-exchange column. The practical advantages of this procedure are described. Finally, the simplicity of the method raises hopes that the mechanism of depletion can be defined.

Binding Sites↗
PubMed1991

Copper transfer from Rhus vernicifera laccase.

Tree laccase, a multi-copper oxidase, has been studied as a copper donor in conjunction with the demetalated forms of three blue copper proteins. Copper transfer could be observed under reducing conditions in the absence of air. Only about 10% of the total copper in laccase could be transferred regardless of the amount of acceptor present in solution, hence, the laccase is heterogeneous as isolated. Potential sources of the heterogeneity are considered. After transfer, laccase could be partially resolved into copper-deficient and nearly holoprotein fractions that would not donate copper when recombined with acceptor protein. EPR results in conjunction with thiol titrations indicate that there is no net loss of type 1 copper from laccase but that there is loss of type 2 copper as well as a small amount of type 3 copper. Very little transfer is observed when type 2-depleted laccase is used as the donor. Finally, the implications that these results could have in the elucidation of possibly more physiologically relevant processes are briefly summarized.

Copper↗
PubMed1995

EPR spectra of type 3 copper centers in Rhus vernicifera laccase and Cucumis sativus ascorbate oxidase.

In order to reveal the detailed structure of the trinuclear site composed of type 2 copper and a pair of type 3 copper centers in multicopper oxidases, the action of inhibitors such as azide, thiocyanate, and fluoride on laccase and ascorbate oxidase has been investigated by absorption, CD, and EPR spectroscopies. Anaerobic reactions of inhibitor-treated laccase and ascorbate oxidase with pyrocatechol and L-ascorbate, respectively, gave EPR signals originating from the inhibitor-bound type 3 copper, except for the case of F(-)-laccase. The hyperfine splittings of these EPR signals (Az = 10.10(-3)-18.10(-3) cm-1) were smaller than those of type 2 copper centers (ca. 20.10(-3) cm-1), indicating that type 3 copper has a tetragonal geometry with tetrahedral distortion. The facile detection of a series of the inhibitor-bound type 3 copper centers indicates that the action of the exogenous anionic inhibitors is not only to interfere the access of dioxygen to the trinuclear site, but also to restrain the reduction of type 3 copper by lowering its reduction potential.

Ascorbate Oxidase↗
PubMed1978

Kinetics of the oxidation of Rhus vernicifera stellacyanin by the Co(EDTA)-- ion.

A kinetic study of the oxidation of the copper(I) form of the blue copper protein stellacyanin (St(I) by Co(EDTA)-- has been performed. Observed rate constants approach a saturation limit with increasing [Co(EDTA)--] at pH 7, consistent with a mechanism involving rapid pre-equilibrium oxidant-protein complex formation followed by rate-limiting intramolecular Cu(I) to Co(III) electron transfer: Co(EDTA)-- + St(i Qp in equilibrium Co(EDTA)-- ---St(I) Co(EDTA)-- ---St(I) k2 leads to Co(EDTA)2-- ---St(II) (Qp = 149 M--1, k2 = 0.169 sec--1; 25.1 degrees, pH 7.0 mu 0.5 M (phosphate)). Activation parameters based on k2 (deltaH not equal to = 1.8 kcal/mol, deltaS not equal to = --56 cal/mol-deg) indicate that the electron transfer process is substantially nondiabatic, in marked contrast with results obtained for Co(phen) 3 3+ as the oxidant. Linear kobsd VS. [Co(EDTA)--] plots are reported for the Co(EDTA)-- oxidation of cuprous stellacyanin at pH 10 (k = 8.9 M--1 sec--1; 25.0, pH 10, mu 0.5 M (carbonate); DELTaH not equal to 11.3 kcal/mol, deltaS not equal to = -16 cal/mol-deg) and at pH 7 in the presence of excess EDTA (k = 21.2 M--1 sec--1; 25.1 degree, pH 7.0, mu 0.5 M (phosphate), [EDTA] tot = 5 X 10(--4) M; deltaH not equal to = 5.9 kcal/mol, delta S not equal to = --33 cal/mol-deg). It is concluded that Co(EDTA)-- adopts an electron transfer mechanism similar to that preferred by Co(phen)33+ under conditions where the oxidant is prevented from binding strongly to reduced stellacyanin.

Cobalt↗
PubMed2000

Rhus (Toxicodendron) dermatitis.

This article reviews the current fund of knowledge on poison ivy, poison oak, and poison sumac dermatitis. It is intended as a global summary to provide the primary care provider with the required information and sources for more esoteric academic pursuits. Toxicodendron characteristics, morphology, and biology are reviewed. The overall medical impact is delineated as well as the clinical manifestations, pathophysiology, prevention, and treatment. Historical perspectives are mentioned throughout, as are future trends in research.

Dermatitis, Toxicodendron↗
PubMed1979

Investigation of the structure of the blue copper protein from Rhus vernicifera stellacyanin by 1H nuclear magnetic resonance spectroscopy.

The 270-MHz 1H nuclear magnetic resonance spectra of Cu(II), Cu(I), and apo-stellacyanin are reported and compared. The data indicate that little conformational change occurs on reduction of the protein or on removing the copper ion. In the aromatic region of the spectra of the holoprotein, resonances associated with two freely titrating histidines are observed. Two additional sharp resonances are observed in the spectra of the apostellacyanin which are tentatively assigned to additional histidines. This result requires that not more than two histidines can be ligands since there are only four histidines in the whole protein. The absence of methionine has been reported and is one of the possible causes for the difference between stellacyanin and the other copper blue proteins. A comparison of these data with those available for other blue copper proteins, in conjunction with the sequence information, leads to a proposed structure for the copper site in stellacyanin.

Apoproteins↗