THESIS

4.1 Amylolytic enzymes
Three groups of amylolytic enzymes are commonly distinguished on the
basis of hydrolytic specificity: enzymes specific for the α-(1,4) linkage, those specific
for the α-(1,6) linkage and those that hydrolyze both α-(1,4) and α-(1,6) linkages
without discrimination (Tester et al. 2004).
4.1.1 Enzymes specific for the α-(1,4) linkage
These enzymes, also known as amylase, are subdivided according to
action pattern into: endoenzymes and exoenzymes (Govindasamy et al. 1992).
1) Endoenzymes
The α-amylases (α-(1,4-D-glucan-4-glucanohydrolase, E.C.
3.2.1.1) are present in most living organisms (microorganisms, plants, and
animals),where they hydrolyze starchy substrates to the oligosaccharide level and
capable of random hydrolysis of α-(1,4) linkages in macromolecules. The α-amylases
are small proteins, generally in the molecular weight range of 50,000 – 60,000. The
amino acid sequences of 18 α-amylases are now known (Raimbaud et al. 1989), but
only two crystallographic analyses of the three- dimensional structure of α-amylases
have been published. These concern the Taka-amylase from Aspergillus oryzae
(Matsuura et al. 1984) and the porcine pancreas α-amylases (Buisson et al. 1987).
The pH optimum of the α-amylases is a function of enzyme
origin, and is usually situated in the weakly acid pH zone between 4.8 and 6.9.
Extremes exist, however, such as the acidophilic α-amylases of Bacillus
acidocaldarius (pH 3.5), and the basophilic α-amylases of Bacillus licheniformis (pH
9.0). The presence of Ca 2+ sometimes permits improved stability of the enzyme at
more extreme pH values.
The temperature optimum for activity is also dependent on the
origin of the enzyme. It is usually about 40 – 50 o C, but may reach values of around
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