8. POLYSACCHARIDASES
361
zymatic reaction. A single amylatic attack on one molecule of substrate
will yield two molecules of split products, which will most likely be
different from one another, both of which may again be a substrate for
further amylatic action, and so on until the reaction comes to an end.
This succession of reactions can be represented by the following simplified expression: initial substrate -» intermediate substrates —> end
products.
During the initial stage of the reaction, amylase will act upon substrates that are different from those existing during the final stages, and
the mechanism of action may be different, therefore, during these two
extreme stages. Thus, amylases of different sources which may behave
in an identical fashion during the initial stage, may function differently
during the final stages of the enzymatic degradation; i.e., they may
yield different end products, a phenomenon frequently encountered
and which is of great importance for our comparative considerations.
An explanation for this phenomenon has been given earlier (8). The
action patterns of an amylase are most typical during the initial stage
of the reaction during which the enzyme acts upon the original substrate or on products closely related to it. During this stage the affinity
between enzyme and substrate will not influence the course of the reaction, i.e., the selection of the bonds to be hydrolyzed, but will govern
only the kinetics of the reaction. Assuming that the affinity decreases
continuously during the enzymatic reaction as the molecular weight of
the intermediate substrates becomes smaller (23-25), a point will
eventually be reached at which the affinity becomes so low that the
enzymatic action will cease. For amylases with different substrate
affinities, this end point will occur at different stages of the reaction,
even though the initial action patterns of these enzymes were the
same. It follows that the affinity between amylase and substrate will
determine, at least to some extent, at what size of the split products
the reaction will be arrested, i.e., what the end products will be.
c. a-Amylatic Degradation of Amylose. During the initial stage of
the reaction a rapid random hydrolysis of a-l,4-glucosidic bonds occurs
(26), whereby however the terminal bonds of the original and intermediate linear substrates are resistant to enzymatic attack (27). During
this phase, the iodine-staining capacity of amylose disappears. The number of glucosidic linkages broken to reach this stage of the hydrolysis
differs markedly for amylases from various origins (28), obviously because of their different affinities for the split products. In addition, the
molecular weight of the substrate rapidly decreases until the polysaccharide has been broken down to maltose, maltotriose, and higher
maltodextrins consisting mainly of maltotetraose (27, 29-31). The reac-
361
zymatic reaction. A single amylatic attack on one molecule of substrate
will yield two molecules of split products, which will most likely be
different from one another, both of which may again be a substrate for
further amylatic action, and so on until the reaction comes to an end.
This succession of reactions can be represented by the following simplified expression: initial substrate -» intermediate substrates —> end
products.
During the initial stage of the reaction, amylase will act upon substrates that are different from those existing during the final stages, and
the mechanism of action may be different, therefore, during these two
extreme stages. Thus, amylases of different sources which may behave
in an identical fashion during the initial stage, may function differently
during the final stages of the enzymatic degradation; i.e., they may
yield different end products, a phenomenon frequently encountered
and which is of great importance for our comparative considerations.
An explanation for this phenomenon has been given earlier (8). The
action patterns of an amylase are most typical during the initial stage
of the reaction during which the enzyme acts upon the original substrate or on products closely related to it. During this stage the affinity
between enzyme and substrate will not influence the course of the reaction, i.e., the selection of the bonds to be hydrolyzed, but will govern
only the kinetics of the reaction. Assuming that the affinity decreases
continuously during the enzymatic reaction as the molecular weight of
the intermediate substrates becomes smaller (23-25), a point will
eventually be reached at which the affinity becomes so low that the
enzymatic action will cease. For amylases with different substrate
affinities, this end point will occur at different stages of the reaction,
even though the initial action patterns of these enzymes were the
same. It follows that the affinity between amylase and substrate will
determine, at least to some extent, at what size of the split products
the reaction will be arrested, i.e., what the end products will be.
c. a-Amylatic Degradation of Amylose. During the initial stage of
the reaction a rapid random hydrolysis of a-l,4-glucosidic bonds occurs
(26), whereby however the terminal bonds of the original and intermediate linear substrates are resistant to enzymatic attack (27). During
this phase, the iodine-staining capacity of amylose disappears. The number of glucosidic linkages broken to reach this stage of the hydrolysis
differs markedly for amylases from various origins (28), obviously because of their different affinities for the split products. In addition, the
molecular weight of the substrate rapidly decreases until the polysaccharide has been broken down to maltose, maltotriose, and higher
maltodextrins consisting mainly of maltotetraose (27, 29-31). The reac-