THESIS

Structure and properties: The pullulanases appear to be composed of
a single polypeptide chain (A. aerogenes, molecular weight 143,000), but nothing is
yet known of the three dimensional structure adopted by the latter. Certain tryptophan
groups may be involved in the catalytic action of pullulanase (Jensen and Norman,
1984).
The pH and temperature optimum: Pullulanases and isoamylases
have pH optima for activity between 5 to 7, and temperature optimum between 45 to
55 o C. The presence of a Ca 2+ ion seems to improve the activity of these enzymes,
whereas heavy metals such as Hg 2+ , Zn 2+ , Cu 2+ , Ag 2+ and Co 2+ exert a more or less
marked inhibitory action (Jensen and Norman, 1984).
Action pattern: The pullulanases hydrolyze the α-(1,6) linkages of
starch, glycogen, pullulan, and limit dextrins. However, the precise location of these
α-(1,6) linkages is relatively important, since it strongly influences the ability of the
enzyme to act on this substrates. In particular, the presence of two α-(1,4) linkages
adjacent to the α-(1,6) linkages to be hydrolyzed (6 2 -O-α- maltotriose) is necessary
Kennedy et al. (1987). The isoamylases show some differences when compared to the
pullulanases. They are unable to hydrolyze pullulan and cannot cleaveα-(1,6) linkages
in molecules containing less than three α-(1,4) linkages (Table 9).
Table 9 Characteristics of pullulanase and isoamylases enzymes
Characteristics
Pullulanase
Type of enzymes
A. aerogenes B. cereus
Isoamylase
Cytophaga sp.
Molecular weight 143,000 112,000 120,000
pH optimum 6.5 6.0-6.5 5.0-6.0
Temperature optimum ( o C ) 50 55 45
Pullulan hydrolysis + + -
Source: Kennedy et al. (1987)
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