8. POLYSACCHARIDASES
389
acid inhibition follows a mechanism different from the reaction with
sulfhydryl groups.
The properties of purified ß-amylase from soybeans have been
studied and found to be similar to those of the crystalline enzyme from
sweet potato (222).
6. Conclusions on ß-Amyhses
In contrast to the wide distribution of α-amylases which are found
in practically all animals and plants, the occurrence of /?-amylase is
strictly limited to a few microbial and vegetable origins. The latter are
soybean seeds, sweet potato tubers, and cereal grains, as well as their
malts; but by no means does /5-amylase occur in all cereals. It appears
that the presence of this enzyme follows no specific patterns and its
absence in certain plants has no known harmful effect on their physiological functions. What role then does ß-amylase play in the degradation of starch by plants? Unlike α-amylase, it does not attack native
starch granules, but it enhances and supplements the action of
a-amylase.
An interesting aspect of the role of /3-amylase is its interrelationship
with the phosphorylase system. Such a viewpoint has been clearly
demonstrated by Porter's work (223). This author noted a considerable
inhibition of plant phosphorylase by ß-amylase, an effect which appears
to be threefold. There is degradation of the polysaccharide synthesized
from glucose-1-phosphate by phosphorylase. Secondly, the primer carbohydrate necessary to initiate the polysaccharide synthesis by phosphorylase is partially destroyed, resulting in a slowdown of polysaccharide synthesis. And finally, /?-amylase appears to exert an inhibitory
action upon phosphorylase which is independent of the two effects upon
carbohydrate. Even more interesting is the observation by the same
author that the presence of /?-amylase changes the type of polysaccharide synthesized by phosphorylase from glucose-1-phosphate. Thus,
in the presence of low concentrations of glucose-1-phosphate, a polysaccharide was obtained which stained red-purple with iodine when
phosphorylase action was primed with achroic dextrins. A lengthening
of the polysaccharide chains to produce a blue-staining polymer could
be obtained by two different ways. First, by further addition of glucose1-phosphate to the digest, and second, without additional glucose-1phosphate but with the addition of ß-amylase in amounts that were
partially inhibitory.
A purely hypothetical but interesting interpretation of the above
observations would be a possible mechanism of regulating the synthesis
of the starch polysaccharides in preventing amylopectin from becoming
glycogen. The latter polysaccharide, which has a higher degree of
389
acid inhibition follows a mechanism different from the reaction with
sulfhydryl groups.
The properties of purified ß-amylase from soybeans have been
studied and found to be similar to those of the crystalline enzyme from
sweet potato (222).
6. Conclusions on ß-Amyhses
In contrast to the wide distribution of α-amylases which are found
in practically all animals and plants, the occurrence of /?-amylase is
strictly limited to a few microbial and vegetable origins. The latter are
soybean seeds, sweet potato tubers, and cereal grains, as well as their
malts; but by no means does /5-amylase occur in all cereals. It appears
that the presence of this enzyme follows no specific patterns and its
absence in certain plants has no known harmful effect on their physiological functions. What role then does ß-amylase play in the degradation of starch by plants? Unlike α-amylase, it does not attack native
starch granules, but it enhances and supplements the action of
a-amylase.
An interesting aspect of the role of /3-amylase is its interrelationship
with the phosphorylase system. Such a viewpoint has been clearly
demonstrated by Porter's work (223). This author noted a considerable
inhibition of plant phosphorylase by ß-amylase, an effect which appears
to be threefold. There is degradation of the polysaccharide synthesized
from glucose-1-phosphate by phosphorylase. Secondly, the primer carbohydrate necessary to initiate the polysaccharide synthesis by phosphorylase is partially destroyed, resulting in a slowdown of polysaccharide synthesis. And finally, /?-amylase appears to exert an inhibitory
action upon phosphorylase which is independent of the two effects upon
carbohydrate. Even more interesting is the observation by the same
author that the presence of /?-amylase changes the type of polysaccharide synthesized by phosphorylase from glucose-1-phosphate. Thus,
in the presence of low concentrations of glucose-1-phosphate, a polysaccharide was obtained which stained red-purple with iodine when
phosphorylase action was primed with achroic dextrins. A lengthening
of the polysaccharide chains to produce a blue-staining polymer could
be obtained by two different ways. First, by further addition of glucose1-phosphate to the digest, and second, without additional glucose-1phosphate but with the addition of ß-amylase in amounts that were
partially inhibitory.
A purely hypothetical but interesting interpretation of the above
observations would be a possible mechanism of regulating the synthesis
of the starch polysaccharides in preventing amylopectin from becoming
glycogen. The latter polysaccharide, which has a higher degree of