360
PETER BERNFELD
phenomena, Kuhn (20) termed the two enzymes a- and ß-amylases,
respectively.
The reduction of viscosity, the change of iodine-staining properties,
and the decrease in glycogen turbidity are consequences of the rapid
transformation of high molecular weight substrate into lower molecular
weight dextrins by α-amylase. This capacity of amylases is generally
called dextrinogenic activity, in contrast to their ability to form reducing sugars, called saccharogenic activity. Accordingly, Ohlsson (21,
22) called α-amylase dextrinogenic amylase and ß-amylase saccharogenic
amylase.
3. Mechanism of a-Amylase Action
The action patterns of amylases are far more complicated than those
of most other enzymes, especially those that act upon well-defined,
homogeneous, and crystallizable substrates of low molecular weight
and that form reaction products with like properties.
a. The Substrate. In contrast to the latter enzymes, amylases do not
act upon a single substrate but rather on a variety of substrates; i.e.,
linear amylose, branched amylopectin, or mixtures of these two; highly
branched glycogen; highly viscous starch pastes; native starch granules;
or soluble starch with varying degrees of degradation, each substrate
having its own mechanism of amylase action. The mechanism of amylase
action is complicated because of the complexity of the chemical and
physical nature of their substrates with respect to degree of branching
and degree of polymerization, and in particular because of the heterogeneity of their substrates with regard to each of these two factors.
Further confusion arises from the fact that some investigators consider
amylose to be a product obtained by a particular process of extraction,
rather than a chemical entity. In the view of these workers amylose
may, therefore, contain certain quantities of the branched constituent
of starch. It is more common and also more logical, however, to consider the term amylose a synonym of the linear a-l,4-glucosidic polysaccharide of starch, i.e., to apply the name of amylose to a chemical
substance. Additional complications in the understanding of amylase
action arise from the fact that amylose has the tendency to aggregate
during standing into larger particles, i.e., to retrogradate during aging
and thus to escape enzymatic attack. This phenomenon is not visible
until precipitation occurs and has often been confused with a resistance
of amylose toward enzymatic action because of a supposed presence
of structural obstacles.
b. Initial and Final Stages of Amylase Action. There occurs a considerable change in the substrate of amylases during the early en-
PETER BERNFELD
phenomena, Kuhn (20) termed the two enzymes a- and ß-amylases,
respectively.
The reduction of viscosity, the change of iodine-staining properties,
and the decrease in glycogen turbidity are consequences of the rapid
transformation of high molecular weight substrate into lower molecular
weight dextrins by α-amylase. This capacity of amylases is generally
called dextrinogenic activity, in contrast to their ability to form reducing sugars, called saccharogenic activity. Accordingly, Ohlsson (21,
22) called α-amylase dextrinogenic amylase and ß-amylase saccharogenic
amylase.
3. Mechanism of a-Amylase Action
The action patterns of amylases are far more complicated than those
of most other enzymes, especially those that act upon well-defined,
homogeneous, and crystallizable substrates of low molecular weight
and that form reaction products with like properties.
a. The Substrate. In contrast to the latter enzymes, amylases do not
act upon a single substrate but rather on a variety of substrates; i.e.,
linear amylose, branched amylopectin, or mixtures of these two; highly
branched glycogen; highly viscous starch pastes; native starch granules;
or soluble starch with varying degrees of degradation, each substrate
having its own mechanism of amylase action. The mechanism of amylase
action is complicated because of the complexity of the chemical and
physical nature of their substrates with respect to degree of branching
and degree of polymerization, and in particular because of the heterogeneity of their substrates with regard to each of these two factors.
Further confusion arises from the fact that some investigators consider
amylose to be a product obtained by a particular process of extraction,
rather than a chemical entity. In the view of these workers amylose
may, therefore, contain certain quantities of the branched constituent
of starch. It is more common and also more logical, however, to consider the term amylose a synonym of the linear a-l,4-glucosidic polysaccharide of starch, i.e., to apply the name of amylose to a chemical
substance. Additional complications in the understanding of amylase
action arise from the fact that amylose has the tendency to aggregate
during standing into larger particles, i.e., to retrogradate during aging
and thus to escape enzymatic attack. This phenomenon is not visible
until precipitation occurs and has often been confused with a resistance
of amylose toward enzymatic action because of a supposed presence
of structural obstacles.
b. Initial and Final Stages of Amylase Action. There occurs a considerable change in the substrate of amylases during the early en-