378
PETER BERNFELD
may thus delay the arrival of the achroic point. Depending largely on
the over-all rate of enzyme hydrolysis, this phenomenon would be more
important at high enzyme concentrations at which the amylose has little
chance to retrogradate, whereas low enzyme concentrations would favor
the formation of enzyme-resistant, retrogradated amylose (188). In the
light of this explanation, the data of Kung et al. may not have much
meaning.
If not caused by retrogradation, however, this phenomenon may be
due to actual differences in the enzyme-substrate affinities for various aamylases, causing differences in the products of the enzyme reaction, beginning at and during the intermediate stages of α-amylatic degradation.
(3). The final stage of a-amylase action. Although the differences between various α-amylases with regard to enzyme-substrate affinities may
begin to manifest themselves during the intermediate stages of enzyme
action, they will become even more important during the final stages,
thus governing the nature of the end products of exhaustive enzymatic
digestion. Some of the results on the end products with the use of pure
enzymes are shown in Table IX. Obviously, α-amylase of A. oryzae yields
three times as much dextrin having a 2.5 times higher degree of
polymerization than pig pancreatic amylase, and malt amylase assumes
an intermediate position. It would appear, therefore, that the pig pancreatic enzyme has a higher affinity for the substrate (in this case the
low molecular weight dextrins) than malt amylase; this is in agreement
with the higher Michaelis-Menten constant of the latter enzyme shown
in the last column of Table IX.
It appears, therefore, that the mode of action of α-amylases from
different sources on a given substrate is the same, but that the influence
of their different enzyme-substrate afBnities becomes more and more
important as the enzymatic reaction proceeds and as the molecular
weight of the substrate decreases. The enzyme-substrate afBnities appear
to vary with the origin of the α-amylases, thus causing differences in
the end products and possibly also in the dextrins appearing during the
intermediate stages.
b. Properties of the Enzyme
(1). Enzymatic properties of a-amylase. These are listed in Table X.
Most of the data have been obtained with the pure crystalline enzymes.
There appears to be a distinct difference between the animal a-amylases
and those of plant or microbial origin; the latter have a lower ratio of
specific activity per protein, a lower pH optimum of activity than the
former, and do not require chloride for their activity.
(2). Physicochemical properties. As shown in Table XI, the solubility
in water exhibits a similar differentiation between amylases from animal
PETER BERNFELD
may thus delay the arrival of the achroic point. Depending largely on
the over-all rate of enzyme hydrolysis, this phenomenon would be more
important at high enzyme concentrations at which the amylose has little
chance to retrogradate, whereas low enzyme concentrations would favor
the formation of enzyme-resistant, retrogradated amylose (188). In the
light of this explanation, the data of Kung et al. may not have much
meaning.
If not caused by retrogradation, however, this phenomenon may be
due to actual differences in the enzyme-substrate affinities for various aamylases, causing differences in the products of the enzyme reaction, beginning at and during the intermediate stages of α-amylatic degradation.
(3). The final stage of a-amylase action. Although the differences between various α-amylases with regard to enzyme-substrate affinities may
begin to manifest themselves during the intermediate stages of enzyme
action, they will become even more important during the final stages,
thus governing the nature of the end products of exhaustive enzymatic
digestion. Some of the results on the end products with the use of pure
enzymes are shown in Table IX. Obviously, α-amylase of A. oryzae yields
three times as much dextrin having a 2.5 times higher degree of
polymerization than pig pancreatic amylase, and malt amylase assumes
an intermediate position. It would appear, therefore, that the pig pancreatic enzyme has a higher affinity for the substrate (in this case the
low molecular weight dextrins) than malt amylase; this is in agreement
with the higher Michaelis-Menten constant of the latter enzyme shown
in the last column of Table IX.
It appears, therefore, that the mode of action of α-amylases from
different sources on a given substrate is the same, but that the influence
of their different enzyme-substrate afBnities becomes more and more
important as the enzymatic reaction proceeds and as the molecular
weight of the substrate decreases. The enzyme-substrate afBnities appear
to vary with the origin of the α-amylases, thus causing differences in
the end products and possibly also in the dextrins appearing during the
intermediate stages.
b. Properties of the Enzyme
(1). Enzymatic properties of a-amylase. These are listed in Table X.
Most of the data have been obtained with the pure crystalline enzymes.
There appears to be a distinct difference between the animal a-amylases
and those of plant or microbial origin; the latter have a lower ratio of
specific activity per protein, a lower pH optimum of activity than the
former, and do not require chloride for their activity.
(2). Physicochemical properties. As shown in Table XI, the solubility
in water exhibits a similar differentiation between amylases from animal