Laccases from Rhus vernicifera

Coniferyl alcohol was polymerized by laccase catalyst. The polymerization behavior depended on the origin of the enzyme. PCL and laccase from Coriolus versicolar showed high catalytic activity to give the dehydrogenative insoluble polymer, whereas very low catalytic activity was observed in laccase from Rhus vernicifera Stokes.54 The increase of the molecular weight was observed in the treatment of soluble lignin using TVL catalyst.82... 

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... 

The redox potential of the Tl Cu-site has been determined using potentiometric titrations with redox mediators for a large number of different laccases and varies between 410 mV vs. NHE for Rhus vernicifera [67] and 790 mV for laccases from Polyporus versicolor and Coriolus hirsutus [244,251]. The T2 and T3 sites have higher potentials [251]. 

Faced with the problem of elucidating the individual roles of the diflFerent copper centers in the blue oxidases, the researcher has naturally focused in recent years on the laccases (9). Being easier to isolate, better characterized, and containing fewer copper atoms than cemloplasmin or ascorbate oxidase, the laccases from the Japanese lacquer tree Rhus vernicifera and the fungus Polyporus versicolor have been the subject of several transient kinetic studies in the millisecond range, that is, studies using stopped-flow spectrophotometry and rapid-freeze EPR spectroscopy (9,49,50). 

Laccases do not possess hydroxylating properties. They oxidize o-diphenols and p-diphenols by a radicalic mechanism. Enzymes of this type were first obtained from the Japanese lack tree Rhus vernicifera. Laccases contain 4 atoms of copper 2 Cu+ ions and 2 Cu + ions. One of the latter is responsible for the blue color of the enzymes. This Cu + ion is reduced by the substrate to Cu+, i.e., it has the properties of an electron carrier (as is the case with iron in dioxygenases and some monooxygenases, C 2.5 and C 2.6). Hence laccases are capable of producing radicals from phenols according to the following equation ... 

Rhus vernicifera laccase is known to incorporate four tightly bound copper atoms distributed in three distinct sites. Type 1 copper is responsible for the intense blue colouration, and a second form of metal ion, type 2, is not associated with any specific spectroscopic absorption bands but has been inferred from e.s.r. studies. This centre is known to function as a strong anion-binding site. Type 3 copper is non-detectable by e.s.r. and is characterized by a u.v. absorption band (Amax ca. 330 nm). Anaerobic stopped-flow studies with hydroquinone (HgQ) have been made to investigate the mode of reduction at these centres. The type 1 and type 3 copper ions are reduced in parallel at comparable rates over a wide range of substrate concentrations and pH. The rate data are consistent with the mechanism... 

The sap of the lacquer trees is the material for Japanese lacquer and is collected from the lacquer trees, Rhus vernicifera, as a latex as a water in oil (urushiol) type emulsion. This sap consists of urushiol (65-70%)(see Fig. 1), plant gum (5-7%), laccase (less than 1%) and water (20-25%). 

Figure 7. (Left) X-band EPR spectra of the Rhus vernicifera tree laccase (a) the resting oxidized form at 2.02 mW and 77 K, (b) the native intermediate at 2.02 mW and 77 K, and (c) the native intermediate taken at 0.5-25 W at 10 K. (Right) Energy diagram of the ground and low-lying doublet states of the native intermediate, with depiction of the origin of the low g-value observed in (c) see text for details. Spectra adapted from [22],...

Wan, YY Du, YM Shi, XW. Immobilization and characterization of laccase from Chinese Rhus vernicifera on modified chitosan. Process Biochemistry, 2006, 41, 1378-1382. 

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