Laccases sources

Laccases Sources and Brief Review of Biochemical and Catalytic Properties. 50... 

Xu F. Dioxygen reactivity of laccase dependence on laccase source, pH, and anion inhibition. Appl Biochem Biotechnol 2001 95 125-133. 

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... 

Table 5.2 contains data about selected copper enzymes from the references noted. It should be understood that enzymes from different sources—that is, azurin from Alcaligenes denitrificans versus Pseudomonas aeruginosa, fungal versus tree laccase, or arthropodan versus molluscan hemocyanin—will differ from each other to various degrees. Azurins have similar tertiary structures—in contrast to arthropodan and molluscan hemocyanins, whose tertiary and quaternary structures show large deviations. Most copper enzymes contain one type of copper center, but laccase, ascorbate oxidase, and ceruloplasmin contain Type I, Type II, and Type III centers. For a more complete and specific listing of copper enzyme properties, see, for instance, the review article by Solomon et al.4... 

It should be noted that some commercial enzyme preparations may contain several enzyme isomers (enzymes derived from one source which belong to the same enzyme class but differ in specificity, stability or other properties). This is most often the case when the commercial preparation was developed for a process industry application rather than a specific chemical biotransformation application. Some fungal enzymes, such as laccase, are sometimes supplied as crude enzyme mixtures. Fungal laccases are manufactured on a huge scale (multitonne per annum) and are principally used in bulk processes such as wood... 

Laccase is perhaps the metallo-enzyme most widely used for this aim. Laccases are a family of multicopper ( blue copper ) oxidases widely distributed in nature Many laccases have fungal origin, while others are produced in plants. They contain four Cu(II) ions, and catalyse the one-electron oxidation of four molecules of a reducing substrate with the concomitant four-electron reduction of oxygen to water . In view of their low redox potential, which is in the range of 0.5-0.8 V vs. NHE depending on the fungal source laccases typically oxidize phenols (phenoloxidase activity) or anilines. 

This chapter will concentrate mainly on structural and functional aspects of these enzymes with the major emphasis on ascorbate oxidase and laccase. Significant progress has been achieved in the last 10 years the determination of amino acid sequences of all three enzymes, each from several sources, and the X-ray structure of ascorbate oxidase. The new information forms the basis of a much deeper understanding of the function of the enzymes as will be demonstrated in this chapter. 

The dominant feature of tyrosinase is that it has both cresolase and catecholase activity. Laccase has a very clear catecholase activity, but its cresolase activity is not so clear. Mason, Fowlks, and Peterson (109) used 02 to label 3,4-dimethylphenol during the tyrosinase-catalyzed oxidation of this compound and showed that the source of the oxygen introduced into the phenol in the phenolase reaction was molecular oxygen according to Reaction 1. 

Laccases from different sources have been coupled to carbon material and recently also to modified gold electrodes [64,67,105,257,258]. For example, laccase was coupled with carbodiimide to a SAM of mercaptopropionic acid gold. A midpoint potential of the immobilized laccase of 410 mV vs. NHE was observed consistent with the potential for the Tl site [67]. DET is most obvious... 

Laccases (p-diphenol O2 oxidoreductase EC 1.10.3.2) catalyze the oxidation of p-diphenols with the concurrent reduction of dioxygen to water. However, the actual substrate specificities of laccases are often quite broad and vary with the source of the enzyme [116,117]. Laccases are members of the blue copper oxidase enzyme family. Members of this family have four cupric (Cu +) ions where each of the known magnetic species (type 1, type 2, and type 3) is associated with a single polypeptide chain. In the blue copper oxidases the Cu + domain is highly conserved and, for some time, the crystallographic structure of ascorbate oxidase, another member of this class of enzymes, has provided a good model for the structure of the laccase active site [124,125]. The crystal structure of the Type-2 Cu depleted laccase from Coprinus cinereus at 2.2. A resolution has also been elucidated [126]. 

Source R Bourbonnais, D Rochefort, MG Paice, S Renaud, D Leech. Development of stable redox complexes to mediate delignification of kraft pulp by laccase. ACS Symposium Series 785 391—399, 2001. With permission. 

The sap from Rhus vemicifera by extraction with light petroleum affords urushiol a mixture which is considerably more sensitive to oxidative deterioration and polymerisation than the cashew phenols since it is both a catechol and even more highly unsaturated. The composition of the sap is to some extent dependent on the source but typically it contains urushiol (55-65%), water (20-30%), glycoprotein (2-3%), polysaccharides (5-7%) and laccase (-c 1%) (ref. 196 ). 

Biological Source Laccase Tyro- Peroxy- Polyphe- Ref. 

Biological Source Laccase Tyro- sinase Peroxy- dase Polyphe- nol oxydase Ref. SO 00... 

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