362
PETER BERNFELD
tion then slows down considerably, but continues until only maltose
(60%) and maltotriose (40%) subsist (27, 32). During this phase,
maltotetraose yields mainly maltose (33), maltopentaose is split into
maltose and maltotriose, while maltohexaose is broken down to two
molecules of maltotriose or, by an alternate mechanism, to maltose and
maltotetraose (34), the latter being further hydrolyzed to maltose.
Finally, in a very slow reaction, maltotriose is split to maltose and
glucose. Thus, the ultimate products of α-amylatic degradation of
amylose are 87% maltose and 13% glucose (8, 27, 33-36). Most of these
observations were made with human salivary, hog pancreatic, or malt
«-amylases.
Some discrepancies between the products obtained during the final
stages of enzyme degradation have appeared in the literature. These
are most likely due either to the presence of branched impurities in
the amylose used for the experiments or to the failure to interpret
properly or to exclude retrogradation of amylose. This latter phenomenon manifests itself by an incomplete enzymatic degradation of amylose
and can be completely eliminated by one or several rejuvenations consisting in alkalinization of the digest, followed by neutralization and
addition of enzyme (37).
d. a-Amylatic Degradation of Amylopectin and Glycogen. Only the
a-l,4-glucosidic linkages of these substrates are hydrolyzed by the
amylases, and all the branching points («-1,6-glucosidic bonds) appear
intact in the end products. As in the case of the α-amylatic degradation
of amylose, amylopectin is broken down into dextrin in a rapid primary
reaction whereby the a-l,4-glucosidic bonds are randomly hydrolyzed.
The terminal bonds of amylose are resistant to «-amylatic attack,
and this is also true for the degradation of amylopectin and glycogen.
In addition, the three a-1,4 links adjacent to the branching links behave
like terminal links and are, in virtue of their position, equally resistant
to hydrolysis by a-amylase (38). During the rapid primary reaction of
the α-amylatic degradation of branched polysaccharides, the absorption
maximum of the iodine complex shifts to lower wavelengths (15) while
the intensity of the light absorption at the maximum decreases and
finally disappears; i.e., the iodine color of amylopectin changes from
purple over red to brown and then disappears, while that of glycogen
just fades out. Simultaneously with the changes occurring in the
iodine complexes, the molecular weight of the substrates rapidly decreases. The average chain length at which the iodine color of amylopectin turns to red (erythro point) or just disappears (achroic point)
depends on various factors, such as the heterogeneity of the original
PETER BERNFELD
tion then slows down considerably, but continues until only maltose
(60%) and maltotriose (40%) subsist (27, 32). During this phase,
maltotetraose yields mainly maltose (33), maltopentaose is split into
maltose and maltotriose, while maltohexaose is broken down to two
molecules of maltotriose or, by an alternate mechanism, to maltose and
maltotetraose (34), the latter being further hydrolyzed to maltose.
Finally, in a very slow reaction, maltotriose is split to maltose and
glucose. Thus, the ultimate products of α-amylatic degradation of
amylose are 87% maltose and 13% glucose (8, 27, 33-36). Most of these
observations were made with human salivary, hog pancreatic, or malt
«-amylases.
Some discrepancies between the products obtained during the final
stages of enzyme degradation have appeared in the literature. These
are most likely due either to the presence of branched impurities in
the amylose used for the experiments or to the failure to interpret
properly or to exclude retrogradation of amylose. This latter phenomenon manifests itself by an incomplete enzymatic degradation of amylose
and can be completely eliminated by one or several rejuvenations consisting in alkalinization of the digest, followed by neutralization and
addition of enzyme (37).
d. a-Amylatic Degradation of Amylopectin and Glycogen. Only the
a-l,4-glucosidic linkages of these substrates are hydrolyzed by the
amylases, and all the branching points («-1,6-glucosidic bonds) appear
intact in the end products. As in the case of the α-amylatic degradation
of amylose, amylopectin is broken down into dextrin in a rapid primary
reaction whereby the a-l,4-glucosidic bonds are randomly hydrolyzed.
The terminal bonds of amylose are resistant to «-amylatic attack,
and this is also true for the degradation of amylopectin and glycogen.
In addition, the three a-1,4 links adjacent to the branching links behave
like terminal links and are, in virtue of their position, equally resistant
to hydrolysis by a-amylase (38). During the rapid primary reaction of
the α-amylatic degradation of branched polysaccharides, the absorption
maximum of the iodine complex shifts to lower wavelengths (15) while
the intensity of the light absorption at the maximum decreases and
finally disappears; i.e., the iodine color of amylopectin changes from
purple over red to brown and then disappears, while that of glycogen
just fades out. Simultaneously with the changes occurring in the
iodine complexes, the molecular weight of the substrates rapidly decreases. The average chain length at which the iodine color of amylopectin turns to red (erythro point) or just disappears (achroic point)
depends on various factors, such as the heterogeneity of the original