384
PETER BERNFELD
B. ß-ÄMYLASES
1. Changes in the Properties of the Substrate Caused by the
Action of the Enzyme
The patterns of the changes in reducing power, viscosity, iodine
staining, and optical rotation of the substrate caused by ß-amylatic degradation are significantly different from those observed during the
action of a-amylase.
a. Increase in Reducing Power. As in the case of α-amylase, each
glucosidic linkage broken by the action of ß-amylase produces one new
aldehyde group. The liberation of maltose as the sole reducing product
resulting from ß-amylatic action can be measured by any method suitable for aldehyde determination.
b. Decrease in Viscosity or Liquefaction of a Starch Paste. Unlike
during «-amylatic degradation, there is only a very slow decrease in the
molecular weight of the substrate during β-amylatic action, yielding
practically no signs of liquefaction of a starch paste nor of viscosity reduction, while the reducing power increases noticeably.
c. Change in the Iodine-Staining Properties. ß-Amylatic breakdown
of amylopectin results in a very slow shift of the absorption maximum
of the iodine-substrate complex to lower wavelengths. The iodine color
of amylopectin or starch does not disappear as during α-amylatic degradation, but turns to purple. When amylose is the substrate, the picture is frequently troubled by the retrogradation of the substrate resulting in water-soluble but enzyme-resistant amylose, which stains
blue with iodine and persists for a long time, sometimes until the end
of the reaction, thus delaying or even preventing the disappearance of
the iodine-staining capacity. In the absence of retrogradation, however,
ß-amylatic breakdown of amylose results in a gradual decrease in the
intensity of the blue iodine color, followed by its complete disappearance.
d. Turbidity. There is no important decrease in the turbidity of
glycogen solutions during ß-amylatic digestion.
e. Change in Optical Rotation. One of the most characteristic properties of /?-amylase is the Waiden inversion that accompanies the hydrolysis. Thus ß-maltose is formed during the enzymatic reaction, and
consequently there is an upward mutorotation (195a).
2. Nomenclature
The liberation of the reducing sugar in the /^-configuration is the
reason why Kuhn termed this enzyme ß-amylase, in contrast to a-amyl-
PETER BERNFELD
B. ß-ÄMYLASES
1. Changes in the Properties of the Substrate Caused by the
Action of the Enzyme
The patterns of the changes in reducing power, viscosity, iodine
staining, and optical rotation of the substrate caused by ß-amylatic degradation are significantly different from those observed during the
action of a-amylase.
a. Increase in Reducing Power. As in the case of α-amylase, each
glucosidic linkage broken by the action of ß-amylase produces one new
aldehyde group. The liberation of maltose as the sole reducing product
resulting from ß-amylatic action can be measured by any method suitable for aldehyde determination.
b. Decrease in Viscosity or Liquefaction of a Starch Paste. Unlike
during «-amylatic degradation, there is only a very slow decrease in the
molecular weight of the substrate during β-amylatic action, yielding
practically no signs of liquefaction of a starch paste nor of viscosity reduction, while the reducing power increases noticeably.
c. Change in the Iodine-Staining Properties. ß-Amylatic breakdown
of amylopectin results in a very slow shift of the absorption maximum
of the iodine-substrate complex to lower wavelengths. The iodine color
of amylopectin or starch does not disappear as during α-amylatic degradation, but turns to purple. When amylose is the substrate, the picture is frequently troubled by the retrogradation of the substrate resulting in water-soluble but enzyme-resistant amylose, which stains
blue with iodine and persists for a long time, sometimes until the end
of the reaction, thus delaying or even preventing the disappearance of
the iodine-staining capacity. In the absence of retrogradation, however,
ß-amylatic breakdown of amylose results in a gradual decrease in the
intensity of the blue iodine color, followed by its complete disappearance.
d. Turbidity. There is no important decrease in the turbidity of
glycogen solutions during ß-amylatic digestion.
e. Change in Optical Rotation. One of the most characteristic properties of /?-amylase is the Waiden inversion that accompanies the hydrolysis. Thus ß-maltose is formed during the enzymatic reaction, and
consequently there is an upward mutorotation (195a).
2. Nomenclature
The liberation of the reducing sugar in the /^-configuration is the
reason why Kuhn termed this enzyme ß-amylase, in contrast to a-amyl-