THESIS

Action pattern: The amyloglucosidases are exoenzymes that release
β-D-glucose by repeated hydrolysis of the α-(1,4) linkages of α-glucan chains from
the nonreducing end. They also hydrolyze, albeit at a slower rate (10-30 times more
slowly), α-(1,6) and α-(1,3) linkages, which makes them rather unspecific as
enzymes. The rate of hydrolysis also depends on the nature of the linkages adjacent to
the hydrolyzed glycosidic linkage, and on the size and structure of the substrate. More
particularly, long α-glucan chains (amylose and amylopectin) are hydrolyzed more
rapidly than maltodextrins and oligosaccharides (Fogarty, 1983).
These enzymes are the only ones capable of assuring total conversion
of starch to glucose. However, when the concentration of the medium in β-glucose
increases, following hydrolysis of α-glucan chains, the amyloglucosidse are liable to
catalyze the condensation of several glucose units (transglycosylase action),
producing mostly maltose and isomaltoe. Some amyloglucosidases are able to partly
degrade solid starch (starch granules) (Fogarty, 1983 and Abe et al. 1988). This
ability to degrade starch granules may be a property more peculiar to type I
amyloglucosidases, which are capable of adsorption to native starch granules.
Table 10 Characteristics of enzyme amyloglucosidases
Origin of enzyme Molecular weight pH optimum Temperature optimum
( o C)
A. niger I 99,000 4.5 – 5.0 -
A. niger II 112,000 4.5-5.0 -
A. oryzae I 76,000 4.5 60
A. oryzae II 38,000 4.5 50
Source: Mercier (1985)
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