Laccases (E.C. 1.10.3.2 benzenediol: oxygen oxidoreductase) are an interesting group of N glycosylated multicopper blue oxidase enzymes and the widely studied enzyme having a broad range of substrate specificity of both phenolic and non-phenolic compounds. They are widely found in fungi, bacteria plant, insects, and in lichen. They catalyze the oxidation of various phenolic and non-phenolic compounds, with the concomitant reduction of molecular oxygen to water. They could increase productivity, efficiency, and quality of products without a costly investment. This chapter depicts the applications of laccase enzyme from white rot fungi, having various industrial (such as textile dye bleaching, paper and pulp bleaching, food includes the baking, it also utilized in fruit juice industry to improve the quality and stabilization of some perishable products having plant oils), pharmaceutical (as it has potential for the synthesis of several useful drugs such anticancerous, antioxidants, synthesis of hormone derivatives because of their high value of oxidation potential) significance.
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The oxidation reactions are essential in several industries. The conventional method of oxidation reactions system have disadvantages like they are non-specific in nature and in which some undesirable side-reactions take place. They also uses environmentally hazardous chemicals. The biological enzymatic oxidation reaction system acts as biodegradable catalyst. They are specific in nature and enzymatic reactions are carried out in mild environmental conditions, acting as biodegradable catalyst. Therefore, laccases (benzenediol: oxygen oxidoreductase; EC 1.10.3.2) have potential for the above mentioned purposes (Couto, Toca, & Herrera, 2006). They oxidize polyphenols, methoxy-substituted phenols, diamines and a considerable range of other compounds except tyrosine (as do the tyrosinases) (Thurston, 1994).They are extensively distributed in fungi. They occur mostly in ascomycetes, deuteromycetes and basidiomycetes. According to mode of action of wood decaying fungi, they are categorized into soft rot fungi, brown rot and white rot. Soft rot belongs to ascomycetes group whereas brown and white rot belongs to basidiomycetes. White rot fungi, degrade lignocellulosic substrate which leaves a white rot residue during the degradation of lignin, hence known as white rot fungi (Kushwaha, Agarwal, Gupta, Maurya, Chaurasia, Singh, & Singh, 2017). In addition to fungi, plants and bacteria, the presence of laccases have also been reported in wasp venom as well as in insects. More or less, all white rot fungi are the laccase producers such as (except for Phanerochaete chrysosporium)Pleurotus ostreatus, Coriolus sanguineus, Trametes hirsuta, Trametes vercicolour, Trametes villosa, Coriolopsis polyzona, Phlebia radiate, Podospora anserine, Lentinus tigrinus, Pleurotus eryngii, Fomes durrismus, Pleurotus sajor caju, Trametes trogii, etc. Some of the examples of laccase producing bacteria are Azospirrullum lipoferum (first laccase producing bacteria), Streptomyces, Anabaena azollae and Actinobacteria . They are thermally more stable than fungal laccases. They are also stable at high pH and high concentrations of chloride and copper ions (Chaurasia, Bharati, Sharma, Singh, Yadav, & Yadava, 2015). They are dimeric or tetrameric glycoprotein, which contains four copper atoms per monomer distributed in three redox sites (Gianfreda, Xu, & Bollag, 1999). Laccase was first described by Yoshida. He extracted it from the exudates of the Japanese lacquer tree Rhus vernicifera (Yoshida 1883). In 1985, Bertrand discovered their characteristic as a metal containing oxidase whereas in the year 1896, both Bertrand and Laborde observed the presence of laccase in fungi for the first time (Desai & Nityanand 2011). Extracellular fungal laccases are extracellular proteins which has the molecular size of approximately 60–70 kDa and with acidic isoelectric point around pH 4.0(Baldrian 2006). These enzymes are more likely stable in extracellular role because they are often produced as highly glycosylated derivatives in which the carbohydrate moieties increase their hydrophilicity. They are generally glycosylated, with an extent of glycosylation ranging between 10 and 25% and only in a few cases higher than 30% (Shleev, Morozova, & Nikitina, 2004; De Souza, & Peralta, 2003). These promising features may contribute to the high stability of the enzyme (Dur´an, Rosa, D’Annibale, & Gianfreda, 2002). Most of the fungal laccases are monomeric proteins. However, few of them exhibit a homodimeric structure, in which the enzyme are being composed of two identical subunits with molecular weight typical for monomeric laccases, e.g., in Phellinus ribis (Min, Kim, Kim, Jung, & Hah, 2001), Pleurotus pulmonarius (De Souza, & Peralta, 2003), Trametes villosa (Yaver, Xu, Golightly, Brown, Brown, & Rey, 1996) and the mycorrhizal fungus Cantharellus cibarius (Palmieri, Giardina, Bianco, Scaloni, Capassoi, & Sannia, 1997).The electrons are removed from the reducing substrate molecules and transferred to oxygen in order to form water without the step of hydrogen peroxide formation (Ducros, Brzozowski, Wilson, Brown, Stergard, Schneider, Yaver, Pedersen, & Davies, 1998). Laccases have a wide substrate range which can serve industrial purposes. The simple requirements of laccase catalysis (presence of substrate and O2), its apparent stability and lack of inhibition (as has been observed with H2O2 for peroxidase), make this enzyme both suitable and attractive for nutitional, industrial and pharmaceutical applications. In addition, laccase can oxidize a wide range of organic and inorganic substrates, including mono, di, polyphenols, aminophenols, methoxyphenols as well as metal complexes which are the major reason for their attractiveness for dozens of biotechnological applications (Upadhayay, Shrivastava, & Agrawal, 2016).