9.4.3.4 Pullulan Type II Hydrolase (Isopullulanase,
Pullulan-4-Glucanohydrolase, EC 3.2.1.57)
Pullulan type II hydrolase enables the constitution of isopanose
(6-0-α-maltosylglucose) units by hydrolyzing the α-1,4 links in the structure of the
pullulan (Niehaus et al. 2000).
Contrary to neopullulanases, this enzyme does not hydrolyze starch or dextran
(Van der Maarel et al. 2002; Hii et al. 2012).
9.4.3.5 Pullulan Type III Hydrolase (EC 3.2.1._)
Pullulan type III hydrolases produce maltotriose, panose, maltose, and glucose units
by hydrolyzing the α-1,4 and α-1,6 glycosidic linkages in the structure of pullulan
(Li et al. 2015; Liu et al. 2016). They also convert starch, amylose, amylopectin,
glycogen, and cyclodextrin to maltose and maltotriose (Van der Maarel et al. 2002;
Hii et al. 2012).
While the type I and II pullulanase and type I pullulanan hydrolase enzymes are
produced by bacteria and archaea, types II and III pullulan hydrolases are produced
respectively by fungi and hyperthermophilic archaea (Nisha and Satyanarayana
2016).
9.4.4 Proteases (EC 3.4)
Proteases are another group of enzymes that are involved in the pretreatment of
lignocellulosic biomass (Srivastava et al. 2020) and microalgae (Carrillo-Reyes et al.
2016). Proteases belonging to the glycoside hydrolase family are at the top of the
global enzyme market (Rao et al. 1998; Haki and Rakshit 2003). They have a wide
substrate specification (Mienda et al. 2014) and catalyze the cleavage of the peptide
linkages in proteins (Theron and Divol 2014; Elleuche et al. 2015).
They are divided into two main groups regarding the location of the peptide
linkage they affect: exopeptidases (aminopeptidases and carboxypeptidases) and
endopeptidases (serine proteases, sistein/thiol proteases, aspartic/acid proteases,
threonine proteases, and metalloproteases) (Rao et al. 1998; Pushpam et al. 2011;
Gurumallesh et al. 2019). Certain protease synthesizers are included in Fig. 9.6
(Arifeen et al. 2009; Choi et al. 2014).
Proteases are typically used in the biofuel production to generate a nitrogen
source for the fermentation of the yeast. Besides, they can contribute to the fermentation by separating starch-gluten complexes, increasing the accessibility of the
amylases to the starch, and changing the chemistry of the grain (Alvarez et al.
2010; Bhari and Singh 2016).
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Pullulan-4-Glucanohydrolase, EC 3.2.1.57)
Pullulan type II hydrolase enables the constitution of isopanose
(6-0-α-maltosylglucose) units by hydrolyzing the α-1,4 links in the structure of the
pullulan (Niehaus et al. 2000).
Contrary to neopullulanases, this enzyme does not hydrolyze starch or dextran
(Van der Maarel et al. 2002; Hii et al. 2012).
9.4.3.5 Pullulan Type III Hydrolase (EC 3.2.1._)
Pullulan type III hydrolases produce maltotriose, panose, maltose, and glucose units
by hydrolyzing the α-1,4 and α-1,6 glycosidic linkages in the structure of pullulan
(Li et al. 2015; Liu et al. 2016). They also convert starch, amylose, amylopectin,
glycogen, and cyclodextrin to maltose and maltotriose (Van der Maarel et al. 2002;
Hii et al. 2012).
While the type I and II pullulanase and type I pullulanan hydrolase enzymes are
produced by bacteria and archaea, types II and III pullulan hydrolases are produced
respectively by fungi and hyperthermophilic archaea (Nisha and Satyanarayana
2016).
9.4.4 Proteases (EC 3.4)
Proteases are another group of enzymes that are involved in the pretreatment of
lignocellulosic biomass (Srivastava et al. 2020) and microalgae (Carrillo-Reyes et al.
2016). Proteases belonging to the glycoside hydrolase family are at the top of the
global enzyme market (Rao et al. 1998; Haki and Rakshit 2003). They have a wide
substrate specification (Mienda et al. 2014) and catalyze the cleavage of the peptide
linkages in proteins (Theron and Divol 2014; Elleuche et al. 2015).
They are divided into two main groups regarding the location of the peptide
linkage they affect: exopeptidases (aminopeptidases and carboxypeptidases) and
endopeptidases (serine proteases, sistein/thiol proteases, aspartic/acid proteases,
threonine proteases, and metalloproteases) (Rao et al. 1998; Pushpam et al. 2011;
Gurumallesh et al. 2019). Certain protease synthesizers are included in Fig. 9.6
(Arifeen et al. 2009; Choi et al. 2014).
Proteases are typically used in the biofuel production to generate a nitrogen
source for the fermentation of the yeast. Besides, they can contribute to the fermentation by separating starch-gluten complexes, increasing the accessibility of the
amylases to the starch, and changing the chemistry of the grain (Alvarez et al.
2010; Bhari and Singh 2016).
280
T. Karaytuğ et al.