8. POLYSACCHARIDASES
387
mercial bacterial a-amylase or of malt a-amylase. The authors concluded that the extract contains a mixture of a- and ß-amylases, and
they have actually shown different pH optima for dextrinizing and saccharifying activity. The possibility of the presence of a phosphorylase
has not been ruled out.
/?-Amylase in molds has been reported to occur in Rhizopus japonicus (158). These findings are based mainly on different pH optima of
the extract for the liquefaction and the saccharification of starch.
5. Properties of and Comparison between Various ß-Amylases
The ß-amylases from two different sources, i.e., sweet potato (207)
and barley malt (210), have been obtained in the pure and crystalline
form; the properties of ß-amylases from other cereals have been reported to resemble closely those of barley malt ß-amylase (197), with
the exception perhaps of differences in the heat stabilities. The latter
property must be considered, however, as being largely conditioned by
environmental factors, rather than as a representative characteristic of
the enzyme. Thus, metal ions and certain proteins, present in crude
or partially purified enzyme extracts, may act as heat stabilizers, as
has been observed with bacterial a-amylase (8, 193). ß-Amylases from
bacterial and mold origin have not been characterized in detail, with
the exception of their pH optima of action.
The properties of the two pure β-amylases are listed in Table XVI
and can be compared to the corresponding data for α-amylases in
Tables IX-XIII. The most important property of /?-amylase, which
permits differentiation of this enzyme from α-amylase, is, of course,
its high ratio of saccharifying to dextrinizing activity; this ratio is more
than six times higher for ß-amylases than for the pure a-amylases
(Table IX). The pH optimum of action, though considerably lower
than that of α-amylases from nonanimal origins, does not appear to be
significantly different from cereal α-amylases (Table X).
A very obvious difference between barley malt a- and ß-amylases
can be visualized by the so-called Wijsman agar plate test (215), which
is based upon the difference in the diffusion constants of the two enzymes. β-Amylase, when applied together with α-amylase as a spot in
the center of an agar plate containing soluble starch, diffuses faster than
a-amylase, thus leaving a circular field in the center of the plate where
the starch was broken down by both enzymes. This central field is surrounded by a ring where ß-amylase alone was acting on the substrate.
Upon developing the plate with iodine, a colorless central area (combined a- and β-amylase action) is separated from the outer dark blue
field (no enzyme action) by a purple ring (ß-amylase action).
387
mercial bacterial a-amylase or of malt a-amylase. The authors concluded that the extract contains a mixture of a- and ß-amylases, and
they have actually shown different pH optima for dextrinizing and saccharifying activity. The possibility of the presence of a phosphorylase
has not been ruled out.
/?-Amylase in molds has been reported to occur in Rhizopus japonicus (158). These findings are based mainly on different pH optima of
the extract for the liquefaction and the saccharification of starch.
5. Properties of and Comparison between Various ß-Amylases
The ß-amylases from two different sources, i.e., sweet potato (207)
and barley malt (210), have been obtained in the pure and crystalline
form; the properties of ß-amylases from other cereals have been reported to resemble closely those of barley malt ß-amylase (197), with
the exception perhaps of differences in the heat stabilities. The latter
property must be considered, however, as being largely conditioned by
environmental factors, rather than as a representative characteristic of
the enzyme. Thus, metal ions and certain proteins, present in crude
or partially purified enzyme extracts, may act as heat stabilizers, as
has been observed with bacterial a-amylase (8, 193). ß-Amylases from
bacterial and mold origin have not been characterized in detail, with
the exception of their pH optima of action.
The properties of the two pure β-amylases are listed in Table XVI
and can be compared to the corresponding data for α-amylases in
Tables IX-XIII. The most important property of /?-amylase, which
permits differentiation of this enzyme from α-amylase, is, of course,
its high ratio of saccharifying to dextrinizing activity; this ratio is more
than six times higher for ß-amylases than for the pure a-amylases
(Table IX). The pH optimum of action, though considerably lower
than that of α-amylases from nonanimal origins, does not appear to be
significantly different from cereal α-amylases (Table X).
A very obvious difference between barley malt a- and ß-amylases
can be visualized by the so-called Wijsman agar plate test (215), which
is based upon the difference in the diffusion constants of the two enzymes. β-Amylase, when applied together with α-amylase as a spot in
the center of an agar plate containing soluble starch, diffuses faster than
a-amylase, thus leaving a circular field in the center of the plate where
the starch was broken down by both enzymes. This central field is surrounded by a ring where ß-amylase alone was acting on the substrate.
Upon developing the plate with iodine, a colorless central area (combined a- and β-amylase action) is separated from the outer dark blue
field (no enzyme action) by a purple ring (ß-amylase action).