394
PETER BERNFELD
of glucose, which, in animals, is more rapidly absorbed through the cell
walls and which is essential for carbohydrate metabolism.
There appears to be no significant difference between the end products of the combined action of α-amylase and maltase on starch taking
place in the intestinal tracts of animals and the direct action of glucamylase alone. The action of the latter enzyme represents an alternate
pathway used by lower organisms; it achieves the same task and yields
the same final products.
Mammalian a-l,6-glucosidase (amylo-l,6-glucosidase) is necessary to
supplement phosphorylase action during its degradative phase, whereas
the other enzymes specific for a-l,6-bonds apparently serve to remove
the obstacles, encountered by the amylases in the form of branching
points in amylopectin. Here again, there appears to be no significant
difference in the end products whether the glucosidase acts upon the
high molecular substrate and achieves the degradation alone or whether
it is an oligosaccharase, called oligo-l,6-glucosidase, of the type found
in the intestinal mucosa, which acts in conjunction with amylases. Apparently, the higher organisms prefer the pathway in which high
molecular substrates are broken down by a first enzyme to low molecular weight dextrins which in turn are broken down further by a second
set of enzymes, as in the amylase-maltase, and the amylase-oligo-1,6glucosidase, systems. Lower organisms appear to have the tendency of
seeking alternate pathways using a single enzyme only, such as glucamylase, or the maltase of C. acetobutylicum.
III. Dextrcmase
Dextran is a bacterial polysaccharide produced by certain microorganisms when grown on a sucrose-containing medium. It has many
analogies with amylopectin (or glycogen); both polysaccharides have
branched structures and are built up from D-glucose units joined together by the same types of bonds, i.e., a-1,4- and a-l,6-glucosidic linkages. The proportion in which the two types of bonds occur in these
polysaccharides is reversed, however. Thus dextran contains mainly
a-l,6-glucosidic linkages, which make up the main chains, while the
branching points are of a-l,4-glucosidic and, in some cases, of the a-1,3glucosidic nature. In spite of the fact that amylopectin and dextran
contain the same type of bonds, their biological degradation is carried
out by completely separate enzyme systems. Amylases are known not to
hydrolyze any bonds in dextran (241), and limit dextrinase action on
dextran has been found to be extremely slow (239), although isomaltose
was hydrolyzed rapidly by the latter enzyme.
Hydrolytic enzymes that digest specifically dextran have been recog-
PETER BERNFELD
of glucose, which, in animals, is more rapidly absorbed through the cell
walls and which is essential for carbohydrate metabolism.
There appears to be no significant difference between the end products of the combined action of α-amylase and maltase on starch taking
place in the intestinal tracts of animals and the direct action of glucamylase alone. The action of the latter enzyme represents an alternate
pathway used by lower organisms; it achieves the same task and yields
the same final products.
Mammalian a-l,6-glucosidase (amylo-l,6-glucosidase) is necessary to
supplement phosphorylase action during its degradative phase, whereas
the other enzymes specific for a-l,6-bonds apparently serve to remove
the obstacles, encountered by the amylases in the form of branching
points in amylopectin. Here again, there appears to be no significant
difference in the end products whether the glucosidase acts upon the
high molecular substrate and achieves the degradation alone or whether
it is an oligosaccharase, called oligo-l,6-glucosidase, of the type found
in the intestinal mucosa, which acts in conjunction with amylases. Apparently, the higher organisms prefer the pathway in which high
molecular substrates are broken down by a first enzyme to low molecular weight dextrins which in turn are broken down further by a second
set of enzymes, as in the amylase-maltase, and the amylase-oligo-1,6glucosidase, systems. Lower organisms appear to have the tendency of
seeking alternate pathways using a single enzyme only, such as glucamylase, or the maltase of C. acetobutylicum.
III. Dextrcmase
Dextran is a bacterial polysaccharide produced by certain microorganisms when grown on a sucrose-containing medium. It has many
analogies with amylopectin (or glycogen); both polysaccharides have
branched structures and are built up from D-glucose units joined together by the same types of bonds, i.e., a-1,4- and a-l,6-glucosidic linkages. The proportion in which the two types of bonds occur in these
polysaccharides is reversed, however. Thus dextran contains mainly
a-l,6-glucosidic linkages, which make up the main chains, while the
branching points are of a-l,4-glucosidic and, in some cases, of the a-1,3glucosidic nature. In spite of the fact that amylopectin and dextran
contain the same type of bonds, their biological degradation is carried
out by completely separate enzyme systems. Amylases are known not to
hydrolyze any bonds in dextran (241), and limit dextrinase action on
dextran has been found to be extremely slow (239), although isomaltose
was hydrolyzed rapidly by the latter enzyme.
Hydrolytic enzymes that digest specifically dextran have been recog-