hirsuta, Trametes ochracea, Trametes villosa, Trametes versicolor, Lentinus
tigrinus, Trametes gallica, Cerrena maxima, and Pleurotus eryngii (Ruiz-Duenas
et al. 2013; Munir et al. 2015). Possible roles of laccase in fungi are in pigment
formation, lignin degradation, and detoxification (Kim et al. 2008a, b).
7.2.1.3 Peroxidases
Lignin peroxidases (LiPs) are glycoproteins of approximately 30–50 kDa with pI
ranging from 3.2 to 4.0. It oxidizes the most phenolic compounds through the
generation of phenoxy radicals. Mn peroxidases are glycosylated proteins with pI
ranging from 4.2 to 4.9 and molecular masses ranging from 45 to 47 kDa (Kirk and
Cullen 1998). Mn peroxidase shows the catalytic cycle which is similar to lignin
peroxidases. The reaction involves two-electron oxidation of the heme by H 2 O 2 ,
which is further carried out by reduction of two electrons to the native enzyme
(Hatakka 1994). Versatile peroxidase is the enzyme which comprises the heme
component with peroxidase activity with hybrid molecular structure of lignin peroxidase and Mn peroxidase. It was first described from the white rot fungus
Pleurotus eryngii (Martinez et al. 1996).
7.2.1.4 Cellulose Degrading Enzymes
Cellulases or cellulose degrading enzymes from ascomycetes or basidiomycetes are
categorized into three enzymes which are endoglucanase, exoglucanase, and
β-glucosidases. The mechanism of action of all cellulolytic enzymes is shown in
Table 7.1.
Cellulases are the enzymes which act on the cellulose in sequential manner which
degrade or depolymerize step by step. Terminology for each enzyme: endoglucanase
is endo-1,4-β-glucanase (E.C.3.2.1.4), exoglucanase is exo-1,4-β-D-glucanase
(E.C.3.2.1.176), and β-glucosidase is β-D-glucoside glucohydrolase (E.C.3.2.1.21).
First, the endoglucanase enzyme catalyzes the reaction with cellulose which cleaves
the glycosidic bonds that forms the long chains of the different oligo- and/or
disaccharides. Furthermore, the other enzyme called exoglucanase acts on the long
chain of the oligomers which also acts on the either reducing or nonreducing ends.
Finally, β-D-glucoside glucohydrolase catalyzes the reaction wherein oligo- or
disaccharides are involved and convert into glucose subunits. The glucose molecules
are directly used for the fungal growth and metabolism (Rudakiya 2019; Narra et al.
2020).
7.2.1.5 Hemicellulose Degrading Enzymes
Hemicellulases are the major group of enzymes which catalyze the degradation of
hemicellulose. Specifically, endo-xylanase, β-xylosidase, α-glucuronidase, α-L190
D. M. Rudakiya et al.
tigrinus, Trametes gallica, Cerrena maxima, and Pleurotus eryngii (Ruiz-Duenas
et al. 2013; Munir et al. 2015). Possible roles of laccase in fungi are in pigment
formation, lignin degradation, and detoxification (Kim et al. 2008a, b).
7.2.1.3 Peroxidases
Lignin peroxidases (LiPs) are glycoproteins of approximately 30–50 kDa with pI
ranging from 3.2 to 4.0. It oxidizes the most phenolic compounds through the
generation of phenoxy radicals. Mn peroxidases are glycosylated proteins with pI
ranging from 4.2 to 4.9 and molecular masses ranging from 45 to 47 kDa (Kirk and
Cullen 1998). Mn peroxidase shows the catalytic cycle which is similar to lignin
peroxidases. The reaction involves two-electron oxidation of the heme by H 2 O 2 ,
which is further carried out by reduction of two electrons to the native enzyme
(Hatakka 1994). Versatile peroxidase is the enzyme which comprises the heme
component with peroxidase activity with hybrid molecular structure of lignin peroxidase and Mn peroxidase. It was first described from the white rot fungus
Pleurotus eryngii (Martinez et al. 1996).
7.2.1.4 Cellulose Degrading Enzymes
Cellulases or cellulose degrading enzymes from ascomycetes or basidiomycetes are
categorized into three enzymes which are endoglucanase, exoglucanase, and
β-glucosidases. The mechanism of action of all cellulolytic enzymes is shown in
Table 7.1.
Cellulases are the enzymes which act on the cellulose in sequential manner which
degrade or depolymerize step by step. Terminology for each enzyme: endoglucanase
is endo-1,4-β-glucanase (E.C.3.2.1.4), exoglucanase is exo-1,4-β-D-glucanase
(E.C.3.2.1.176), and β-glucosidase is β-D-glucoside glucohydrolase (E.C.3.2.1.21).
First, the endoglucanase enzyme catalyzes the reaction with cellulose which cleaves
the glycosidic bonds that forms the long chains of the different oligo- and/or
disaccharides. Furthermore, the other enzyme called exoglucanase acts on the long
chain of the oligomers which also acts on the either reducing or nonreducing ends.
Finally, β-D-glucoside glucohydrolase catalyzes the reaction wherein oligo- or
disaccharides are involved and convert into glucose subunits. The glucose molecules
are directly used for the fungal growth and metabolism (Rudakiya 2019; Narra et al.
2020).
7.2.1.5 Hemicellulose Degrading Enzymes
Hemicellulases are the major group of enzymes which catalyze the degradation of
hemicellulose. Specifically, endo-xylanase, β-xylosidase, α-glucuronidase, α-L190
D. M. Rudakiya et al.