Endoamylases are among the most important starch hydrolysing enzymes. They
are of great significance for biotechnology with approximately 25% of the world
enzyme market [7, 8]. Amylases of microbial origin are commercially available and
have replaced the chemical hydrolysis of starch in starch processing industry [9].
The industrial application of amylases has been extensively discussed in several
reviews [2, 6, 8, 10–16].
α-Amylases have been used in a wide range of applications such as in food,
fermentation, textile, paper, detergent, pharmaceutical and fine chemical industries.
With the advances in biotechnology, the amylase applications have expanded in
many fields such as clinical, medicinal and analytical chemistry, as well as their
widespread application in starch saccharification and in the textile, food, brewing
and distilling industries [10–12].
2.2 Exoamylases
Exoamylases act on the external glucose residues of amylose and amylopectin.
These enzymes may either exclusively cleave only the α-1-4 glycosidic bonds to
produce maltose and β-limit dextrin, such as the β-amylase (EC 3.2.1.2), or cleave
both α-1-4 and α-1-6 glycosidic bonds to produce only glucose, such as
amyloglucosidase or glucoamylase (EC 3.2.1.3) and α-glucosidase (EC 3.2.1.20).
β-Amylase and glucoamylase further convert the anomeric configuration of their
products from α- to β-, via an inverting mechanism of bond cleavage. Glucoamylase
and α-glucosidase differ in their substrate preferences, with the former hydrolysing
long-chain polysaccharides more effectively, while the latter preferentially hydrolyses shorter maltoligosaccharides.
Also included in this group of enzymes are cyclodextrin glycosyltransferases
(EC 2.4.1.19), enzymes with an additional transglycosylation function, maltogenic
α-amylase (EC 3.2.1.133) and maltooligosaccharide-forming amylases such as the
maltotetraose-forming enzyme from Pseudomonas stutzeri (EC 3.2.1.60) and the
maltohexaose-forming amylase from Klebsiella pneumoniae (EC 3.2.1.98).
2.3 Debranching Enzyme
This group of enzymes exclusively hydrolyse the α-1-6 glycosidic bonds of amylopectin. They include isoamylase (EC 3.2.1.68) and pullulanase (EC 3.2.1.41) type I,
which, in addition to amylopectin and glycogen, hydrolyse pullulan, a polymer
consisting of repeating units of maltotriose that are linked via α-1-6 glycosidic
bonds. The end products formed are long linear polysaccharides. Pullulanase type
II hydrolyses both α-1-4 and α-1-6 glycosidic bonds to produce maltose and
maltotriose. These enzymes are also referred to as α-amylase-pullulanase or
amylopullulanase. Neopullulanases (EC 3.2.1.135) hydrolyse the α-1-4 glycosidic
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are of great significance for biotechnology with approximately 25% of the world
enzyme market [7, 8]. Amylases of microbial origin are commercially available and
have replaced the chemical hydrolysis of starch in starch processing industry [9].
The industrial application of amylases has been extensively discussed in several
reviews [2, 6, 8, 10–16].
α-Amylases have been used in a wide range of applications such as in food,
fermentation, textile, paper, detergent, pharmaceutical and fine chemical industries.
With the advances in biotechnology, the amylase applications have expanded in
many fields such as clinical, medicinal and analytical chemistry, as well as their
widespread application in starch saccharification and in the textile, food, brewing
and distilling industries [10–12].
2.2 Exoamylases
Exoamylases act on the external glucose residues of amylose and amylopectin.
These enzymes may either exclusively cleave only the α-1-4 glycosidic bonds to
produce maltose and β-limit dextrin, such as the β-amylase (EC 3.2.1.2), or cleave
both α-1-4 and α-1-6 glycosidic bonds to produce only glucose, such as
amyloglucosidase or glucoamylase (EC 3.2.1.3) and α-glucosidase (EC 3.2.1.20).
β-Amylase and glucoamylase further convert the anomeric configuration of their
products from α- to β-, via an inverting mechanism of bond cleavage. Glucoamylase
and α-glucosidase differ in their substrate preferences, with the former hydrolysing
long-chain polysaccharides more effectively, while the latter preferentially hydrolyses shorter maltoligosaccharides.
Also included in this group of enzymes are cyclodextrin glycosyltransferases
(EC 2.4.1.19), enzymes with an additional transglycosylation function, maltogenic
α-amylase (EC 3.2.1.133) and maltooligosaccharide-forming amylases such as the
maltotetraose-forming enzyme from Pseudomonas stutzeri (EC 3.2.1.60) and the
maltohexaose-forming amylase from Klebsiella pneumoniae (EC 3.2.1.98).
2.3 Debranching Enzyme
This group of enzymes exclusively hydrolyse the α-1-6 glycosidic bonds of amylopectin. They include isoamylase (EC 3.2.1.68) and pullulanase (EC 3.2.1.41) type I,
which, in addition to amylopectin and glycogen, hydrolyse pullulan, a polymer
consisting of repeating units of maltotriose that are linked via α-1-6 glycosidic
bonds. The end products formed are long linear polysaccharides. Pullulanase type
II hydrolyses both α-1-4 and α-1-6 glycosidic bonds to produce maltose and
maltotriose. These enzymes are also referred to as α-amylase-pullulanase or
amylopullulanase. Neopullulanases (EC 3.2.1.135) hydrolyse the α-1-4 glycosidic
Starch-Modifying Enzymes
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