1. Introduction
Amylases are enzymes which hydrolyse starch molecules
to give diverse products including dextrins and
progressively smaller polymers composed of glucose
units [1]. These enzymes are of great significance in
present day biotechnology with applications ranging
from food, fermentation, textile to paper industries [2].
Although amylases can be derived from several sources,
including plants, animals and microorganisms, microbial
enzymes generally meet industrial demands. Today
a large number of microbial amylases are available
commercially and they have almost completely replaced
chemical hydrolysis of starch in starch processing
industry [2].
The history of amylases began in 1811 when the first
starch degrading enzyme was discovered by Kirchhoff.
This was followed by several reports of digestive
amylases and malt amylases. It was much later in
1930, that Ohlsson suggested the classification of starch
digestive enzymes in malt as a- and b-amylases according
to the anomeric type of sugars produced by the
enzyme reaction. a-Amylase (1,4-a-D-glucan-glucanhydrolase,
EC. 3.2.1.1) is a widely distributed secretary
enzyme. a-Amylases of different origin have been
extensively studied.
Amylases can be divided into two categories, endoamylases
and exoamylases. Endoamylases catalyse hydrolysis
in a random manner in the interior of the starch
molecule. This action causes the formation of linear and
branched oligosaccharides of various chain lengths.
Exoamylases hydrolyse from the non-reducing end,
successively resulting in short end products. Today a
large number of enzymes are known which hydrolyse
starch molecule into different products and a combined
action of various enzymes is required to hydrolyse
starch completely.
A number of reviews exist on amylases and their
applications, however, none specifically covers a-amy-