Laccase Rhus,

Laccase Rhus vernicifera Cu 2,400 Keilin and Mann (1940b)... 

Cu in ceruloplasmin horse Cu in laccase Rhus succedanea Cu in laccase Rhus vernicifera... 

Laccase was first isolated by Yoshida in 1883 [43] from tree lacquer of Rhus ver-nicifera. Laccases can thus be classified according to their source plant, fungal or, more recently, bacterial or insect [44], The laccase enzyme active site contains four copper ions classified into three types based upon their geometry and coordinating ligands, denoted... 

Rhus Laccase AOT/n-octane Solubilization and catalytic studies [78]... 

On adding dioxygen to the fully reduced laccase of the lacquer tree Rhus vemicifera, the type-1 Cu and the type-3 Cu-pair were oxidized in the ms range and an optical intermediate was observed at 360 nm At liquid helium temperatures an EPR signal was observed, which was tentatively interpreted as due to O ", as a result of its very short relaxation time and of the increase of its linewidth when the reduced laccase of the fungus Polyporus versicolor was treated with 0 A similar paramagnetic oxygen intermediate was also observed with the laccase of another lacquer tree Rhus succedanea and with ceruloplasmin. The decay of the intermediate at 25 °C (tj = 1 s at pH 5.5 with R. succedanea laccase) was accompanied by the reoxidation of the type-2 Cu >. One would expect, however, such an intermediate to be extremely reactive (See Sect. 3.3), while it was stable in tree laccase depleted of type-2 Cu(II)... 

Visible MCD spectra of plastocyanin, azurin, Rhus vernicifera laccase, ascorbate oxidase and ceruloplasmin are similar on a per copper basis, but show differences from those of stellacyanin and fungal laccase. This is of interest in view of the absence of methionine from the coordination sphere of copper in stellacyanin, and the very high redox potential of fungal laccase.925... 

Type III copper(II), found for example in Rhus laccase, is ESR inactive. Although copper(II) is present no ESR spectrum can be obtained. Recent magnetic susceptibility measurements on Rhus laccase indicate an antiferromagnetically coupled cop-per(II) dimer. 

The Reaction of Partially Reduced Rhus laccase with Oxygen... 

Figure 10. Rhus laccase—reduction by 02 and reoxidation by oxygen observed at 614 nm. Solution contained 1.5 X 10 5M enzyme, 1.2 X 10 3 M oxygen, 1% tert-butanol, pH 6.9, 25°. Upper trace ...

The Interaction between Rhus laccase and Hydrogen Peroxide... 

Figure 11. Spectral changes upon anaerobic titration of reduced Rhus laccase with hydrogen peroxide.

Figure 13. Anaerobic titration of Rhus laccase by hydroquinone. 

Fig. 38. Optical absorption spectra (room temperature) of native Rhus vemicifera laccase and native + low 10-fold excess) concentration NJ, high (3100-fold excess) concentration NJ and 30-fold excess peroxide, dialyzed. EPR spectra (77 K v = 9.1 GHz) of native, native + low concentration NJ and native + high concentration NJ...

Fig. 42. Spectroscopically effective active site representations of the coupled binuclear copper site (left) and the type 3 site in Rhus laccase (right) where OR and R represent endogenous protein bridges in the respective sites...

The mechanism of dioxygen reduction at the trinuclear cluster in MCO catalysis has been a strong focus for research on this class of copper oxidases. Dioxygen reduction has been most thoroughly investigated in Rhus laccase (a plant laccase, from the Japanese lacquer tree). The primary reason for using Rhus Lac is the availability of a metal-substituted form the enzyme, a TlHg form, in which the... 

Laccase is widely distributed in plants and fungi. Laccase from higher plants, found in various species of the Chinese, Vietnamese, and Japanese lacquer trees, has been extensively investigated (9). The biological function of laccase in these trees is well understood. The laccase of the lacquer trees (Rhus sp.) is found in white latex, which contains phenols. After injury of the tree, these are oxidized by dioxygen to radicals, which spontaneously polymerize, building a protective structure that closes the wound. 

The presence of this ESR non-detectable copper has been established in other blue copper oxidases including Rhus laccase (60), ceruloplasmin (98), and cytochrome oxidase (99),... 

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