Laccases

The reactions catalyzed by laccases proceed by the monoelectronic oxidation of a suitable substrate molecule (phenols and aromatic or aliphatic amines) to the corresponding reactive radical (Riva, 2006). The redox process takes place with the assistance of a cluster of four copper atoms that form the catalytic core of the enzyme they also confer the typical blue color to these enzymes because of the intense electronic absorption of the Cu-Cu linkages (Piontek et al., 2002). The overall outcome of the catalytic cycle is the reduction of one molecule of oxygen to two molecules of water and the concomitant oxidation of four substrate molecules to produce four 

Research on Enzymes in the Pulp and Paper Industry 6.3.4.1 Laccases 

For this reason, considerable interest has arisen in the pulp and paper industry concerning the potential replacement of traditional bleaching reagents with en- 

---

An oxidative activation of the lignin also can be achieved in a biochemical way by adding enzymes (phenol oxidase laccase) to the spent sulfite liquor, whereby... 

Horse radish peroxidase, H2O2 or Laccase, pH 4, 2% DMSO or DMF. Cleavage occurs by the formation of a phenyldiimide, which decomposes to the acid, nitrogen, and benzene. The laccase method is compatible with the readily oxidized tryptophan and methionine because it does not use peroxide. ... 

Laccase, 6,699 copper, 6,654 cytochrome oxidases concerted electron transfer, 6,683 fungal... 

C13-0112. Fungal laccase is an enzyme found in fungi that live on rotting wood. The enzyme is blue and contains 0.40% by mass copper. The molar mass of the enzyme is approximately 64,000 g/mol. How many copper atoms are there in one molecule of fungal laccase ... 

Kim, J.E. et ah. Putative polyketide synthase and laccase for biosynthesis of auro-fusarin in Gibberella zea, Appl. Environ. Microbiol., 71, 1701, 2005. 

Laccase (PCL) as well as peroxidases (HRP and SBP) induced a new type of oxidative polymerization of the 4-hydroxybenzoic acid derivatives, 3,5-dimethoxy-4-hydroxybenzoic acid (syringic acid) and 3,5-dimethyl-4-hydroxybenzoic acid. The polymerization involved elimination of carbon dioxide and hydrogen from the monomer to give PPO derivatives with molecular weight up to 1.8 x lO (Scheme 22). - ... 

Superoxide anion scavenging activity of the enzymatically synthesized poly(catechin) was evaluated. Poly(catechin), synthesized by HRP catalyst, greatly scavenged superoxide anion in a concentration-dependent manner, and almost completely scavenged at 200 p.M of a catechin unit concentration. The laccase-catalyzed synthesized poly(catechin) also showed excellent antioxidant property. Catechin showed pro-oxidant property in concentrations lower than 300 jlM. These results demonstrated that the enzymatically synthesized poly(catechin) possessed much higher potential for superoxide anion scavenging, compared with intact catechin. 

The conjugation of catechin on poly(allylamine) using ML as catalyst was examined under air. During the conjugation, the reaction mixture turned brown and a new peak at 430 nm was observed in the UV-vis spectrum. At pH 7, the reaction rate was the highest. The conjugation hardly occurred in the absence of laccase, indicating that the reaction proceeded via enzyme catalysis. 

Catechin-immobilizing polymer particles were prepared by laccase-catalyzed oxidation of catechin in the presence of amine-containing porous polymer particles. The resulting particles showed good scavenging activity toward stable free l,l-diphenyl-2-picryl-hydrazyl radical and 2,2 -azinobis(3-ethylbenzothiazoline-6-sulfonate) radical cation. These particles may be applied for packed column systems to remove radical species such as reactive oxygen closely related to various diseases. 

Perez J, TW Jeffries (1990) Mineralization of C-ring-labelled synthetic lignin correlates with the production of lignin peroxidase, not of manganese peroxidase or laccase. Appl Environ Microbiol 56 1806-1812. 

FIGURE 4.8 Reaction between 2,4,5-trichlorophenol and syringic acid catalyzed by laccase. 

Zille A, B Gdrnacka, A Rehorek, A Cavaco-Paulo (2005) Degradation of azo dyes by Trametes villosa laccase over long periods of oxidative conditions. Appl Environ Microbiol 71 6711-6718. 

Laccase active site with proposed mode of substrate / Intermediate binding... 

Figure 17.3 Anatomy of a redox enzyme representation of the X-ray crystallographic structure of Trametes versicolor laccase III (PDB file IKYA) [Bertrand et al., 2002]. The protein is represented in green lines and the Cu atoms are shown as gold spheres. Sugar moieties attached to the surface of the protein are shown in red. A molecule of 2,5-xyhdine that co-crystallized with the protein (shown in stick form in elemental colors) is thought to occupy the broad-specificity hydrophobic binding pocket where organic substrates ate oxidized by the enzyme. Electrons from substrate oxidation are passed to the mononuclear blue Cu center and then to the trinuclear Cu active site where O2 is reduced to H2O. (See color insert.)...

Figure 17.5 The protein environment around the Cu centers (gold spheres) of laccase from Melanocarpus albomyces (PDB file IGWO) showing a substrate O2 molecule bound in the trinuciear Cu site [Hakulinen et al., 2002], The protein is depicted in stick representation with atoms in their conventional coloring. (Courtesy of Armand W. J. W. Tepper.) (See color insert.)...

---