8. POLYSACCHARIDASES
383
amylases have been found to be identical on the basis of chemical and
physical tests (74), and the pancreatic, salivary, serum, kidney, and
spleen α-amylases of the hog were reported to be equal, hog liver
α-amylase is clearly different from all the other porcine amylases (194).
Monkey and human serum amylases gave a similar and limited response
to the antiserum obtained with hog pancreatic amylase, but rat, guinea
pig, and mouse serum amylases were not inhibited by this antiserum, a
result which was to be expected on the basis of the phylogenetic relationships.
The apparent identity in one and the same animal species of the
α-amylases of all tissues and fluids, with the exception of liver amylase,
points to the view that the low levels of α-amylase in serum, urine, lung,
spleen, heart, kidney, brain, duodenum, colon, muscle, etc., represent
mere "leakages" from the main sources; i.e., from pancreas and in some
species from the salivary glands, whereas liver amylase being different
from the others must be synthesized in situ and probably has some
specific function in the physiology of the liver. A possible requirement
of this organ for α-amylase might be the regulation of glycogen synthesis catalyzed by phosphorylase. As is well known, the latter enzyme
requires carbohydrate primers to initiate the reaction. If these primer
carbohydrates were depleted, the glycogen synthesis would either stop
or, in the presence of stored glycogen, would merely further increase
the molecular weight of the latter ad infinitum, while the number of
glycogen molecules would remain constant. The presence of a small
amount of α-amylase is sufficient, however, to produce new primer
molecules and to protect against an increase of the molecular weight
beyond certain limits.
Various enzymatic or physicochemical properties of the pure enzymes
permit distinguishing between the animal α-amylases and those of the
vegetable kingdom. The former have a high specific activity per milligram protein, an optimum of action at pH 6.9, a low solubility in water
and require chloride for activity. On the other side, the plant and microbial α-amylases have lower specific activities per milligram protein, a
pH optimum between 4.7 and 5.9, a ten- to twentyfold higher solubility
in water and do not require chloride.
The mechanism of enzyme action appears to be the same for all
«-amylases during the initial stages of the reaction. As the substrate is
broken down into fragments of considerably smaller molecular weight,
however, the difference in enzyme-substrate affinities between the
α-amylases of various origins starts to become manifest and to cause
differences in the end products remaining after exhaustive starch digestion.
383
amylases have been found to be identical on the basis of chemical and
physical tests (74), and the pancreatic, salivary, serum, kidney, and
spleen α-amylases of the hog were reported to be equal, hog liver
α-amylase is clearly different from all the other porcine amylases (194).
Monkey and human serum amylases gave a similar and limited response
to the antiserum obtained with hog pancreatic amylase, but rat, guinea
pig, and mouse serum amylases were not inhibited by this antiserum, a
result which was to be expected on the basis of the phylogenetic relationships.
The apparent identity in one and the same animal species of the
α-amylases of all tissues and fluids, with the exception of liver amylase,
points to the view that the low levels of α-amylase in serum, urine, lung,
spleen, heart, kidney, brain, duodenum, colon, muscle, etc., represent
mere "leakages" from the main sources; i.e., from pancreas and in some
species from the salivary glands, whereas liver amylase being different
from the others must be synthesized in situ and probably has some
specific function in the physiology of the liver. A possible requirement
of this organ for α-amylase might be the regulation of glycogen synthesis catalyzed by phosphorylase. As is well known, the latter enzyme
requires carbohydrate primers to initiate the reaction. If these primer
carbohydrates were depleted, the glycogen synthesis would either stop
or, in the presence of stored glycogen, would merely further increase
the molecular weight of the latter ad infinitum, while the number of
glycogen molecules would remain constant. The presence of a small
amount of α-amylase is sufficient, however, to produce new primer
molecules and to protect against an increase of the molecular weight
beyond certain limits.
Various enzymatic or physicochemical properties of the pure enzymes
permit distinguishing between the animal α-amylases and those of the
vegetable kingdom. The former have a high specific activity per milligram protein, an optimum of action at pH 6.9, a low solubility in water
and require chloride for activity. On the other side, the plant and microbial α-amylases have lower specific activities per milligram protein, a
pH optimum between 4.7 and 5.9, a ten- to twentyfold higher solubility
in water and do not require chloride.
The mechanism of enzyme action appears to be the same for all
«-amylases during the initial stages of the reaction. As the substrate is
broken down into fragments of considerably smaller molecular weight,
however, the difference in enzyme-substrate affinities between the
α-amylases of various origins starts to become manifest and to cause
differences in the end products remaining after exhaustive starch digestion.