8. POLYSACCHARIDASES
359
with widely varying chain length, the reducing values obtained generally do not reflect an exact picture of the number of free aldehyde
groups present and, hence, of the number of glucosidic bonds split,
unless a technique for reducing groups is employed that is independent
of the chain length of the oligo- or polysaccharide. This is true for the
hypoiodite method of Willstätter and Schudel (11) and modifications
thereof. The dinitrosalicylic acid method of Sumner (12), when maltose
is used as a standard, has also been found to be practically independent
of the chain length of the reducing saccharides, and hence to yield reducing values, which are fairly proportional to the number of reducing
end groups (13), even at rather high molecular weights.
b. Decrease in Viscosity, or Liquefaction. Owing to the extremely
rapid decrease of the giant particle size of a starch paste during
α-amylatic attack, there is a rapid decrease in the viscosity during the
initial stage of enzyme action, while the increase in reducing power is
still hardly noticeable (14).
c. Change in the Iodine-Staining Properties. Owing to the rapid
shortening of straight a-l,4-glucosidic chains of the substrate during
α-amylatic degradation, there occurs a shift of the maximum of light
absorption of the iodine-starch complex to lower wavelengths (15); i.e.,
a shift of the blue iodine color to purple and brown, followed by the
complete disappearance of the capacity to produce a stain with iodine.
The disappearance of the iodine color (achroic point) or its change can
be measured either spectrophotometrically or by comparison with suitable artificial color standard solutions, and can thus be used for the
quantitative determination of α-amylase action (16-19).
d. Decrease in the Turbidity of Glycogen Solutions. This decrease
is due to the rapid decrease of the giant particle size upon a-amylatic
action. It can be measured nephelometrically and thus serve as a
means for activity determination of a-amylase.
e. Change in Optical Rotation. The reducing oligosaccharides are
liberated in their optical «-configuration by the action of α-amylase, as
it is to be expected from the a-l,4-glucosidic nature of these bonds in
the polysaccharides; they undergo a downward mutarotation after their
liberation.
2. Nomenclature
The liberation of the reducing saccharides in their «-configuration
and the downward mutarotation of the reaction mixture are typical for
α-amylatic action and contrast with the behavior of β-amylatic degradation. The latter is accompanied by a Waiden inversion, thus releasing the reducing sugar in the /^-configuration. On the basis of these
359
with widely varying chain length, the reducing values obtained generally do not reflect an exact picture of the number of free aldehyde
groups present and, hence, of the number of glucosidic bonds split,
unless a technique for reducing groups is employed that is independent
of the chain length of the oligo- or polysaccharide. This is true for the
hypoiodite method of Willstätter and Schudel (11) and modifications
thereof. The dinitrosalicylic acid method of Sumner (12), when maltose
is used as a standard, has also been found to be practically independent
of the chain length of the reducing saccharides, and hence to yield reducing values, which are fairly proportional to the number of reducing
end groups (13), even at rather high molecular weights.
b. Decrease in Viscosity, or Liquefaction. Owing to the extremely
rapid decrease of the giant particle size of a starch paste during
α-amylatic attack, there is a rapid decrease in the viscosity during the
initial stage of enzyme action, while the increase in reducing power is
still hardly noticeable (14).
c. Change in the Iodine-Staining Properties. Owing to the rapid
shortening of straight a-l,4-glucosidic chains of the substrate during
α-amylatic degradation, there occurs a shift of the maximum of light
absorption of the iodine-starch complex to lower wavelengths (15); i.e.,
a shift of the blue iodine color to purple and brown, followed by the
complete disappearance of the capacity to produce a stain with iodine.
The disappearance of the iodine color (achroic point) or its change can
be measured either spectrophotometrically or by comparison with suitable artificial color standard solutions, and can thus be used for the
quantitative determination of α-amylase action (16-19).
d. Decrease in the Turbidity of Glycogen Solutions. This decrease
is due to the rapid decrease of the giant particle size upon a-amylatic
action. It can be measured nephelometrically and thus serve as a
means for activity determination of a-amylase.
e. Change in Optical Rotation. The reducing oligosaccharides are
liberated in their optical «-configuration by the action of α-amylase, as
it is to be expected from the a-l,4-glucosidic nature of these bonds in
the polysaccharides; they undergo a downward mutarotation after their
liberation.
2. Nomenclature
The liberation of the reducing saccharides in their «-configuration
and the downward mutarotation of the reaction mixture are typical for
α-amylatic action and contrast with the behavior of β-amylatic degradation. The latter is accompanied by a Waiden inversion, thus releasing the reducing sugar in the /^-configuration. On the basis of these