THESIS

Structure and properties of β- amylase; Knowledge of β-amylase
(α-1,4- glucan maltohydrolase) is still relatively limited. The best known are those
of plant origin (barley, wheat, oats, soya, and sweet potato) synthesized in latent
form I grains and seeds, and then activated by proteolysis during germination.
More recently, β- amylases from bacterial sources (Bacillus, Pseudomonas, and
Streptomyces) have also been isolated (Mercier, 1985). β-amylases are proteins
composed of a single polypeptide chain (Molecular weight 60,000), but amino
acid sequences are presently known for only two (Bacillus polymyxa and soya
seed) (Mikami and Morita, 1988).
The pH and temperature optimum: The β-amylase have a pH
optimum generally between 5 and 6, and a temperature optimum of about 50 o C.
However, bacteria β-amylase show thermo stability properties superior to those of β-
amylase of plant origin (Table 8).
Action pattern of β-amylase; Beta-amylase, or saccharifying
enzymes, hydrolyze α-(1,4) linkages in amylose and amylopectin chains from their
non reducing ends, releasing maltose with a β-anomery. The action of the enzyme is
blocked at the α-(1,6) branch-points. Thus, amylose is totally hydrolyzed, whereas
under the same conditions 55% of the amylopectin is converted to β-maltose. The
residual product of amylopectin hydrolysis is a limit β-dextrin of high molecular
weight, containing all of the α-(1,6) linkages present in the initial molecule (Ray,
1996).
50