8. POLYSACCHARIDASES
391
bond, may occur in common with a glucosidase specific for the other
type, and neither enzyme may have been sufficiently purified to permit
of deciding to which class they actually belong. The following classification is, therefore, only a tentative one.
1. a-l,4-Glucosidases
A glucosidase was detected in the mold Rhizopus delemar (224)
and has been isolated in highly purified form, free of a-amylase (225).
It was called glucamylase and has been found to convert corn amylopectin to 95% theoretical glucose; glycogen to 92% glucose; residual ß
dextrins from amylopectin to 89% glucose, and maltose to 100% glucose
(226). Since α-amylase is absent from the preparations of glucamylase,
glucose cannot result from the action of maltase on degradation products of a primary reaction, but must itself be the primary product of
hydrolysis by this enzyme. The authors believe that glucamylase, like
ß-amylase, attacks the nonreducing ends of the glucosidic chains of its
substrate, and they conclude that this enzyme either hydrolyzes «-1,6glucosidic bonds as well as a-l,4-glucosidic linkages or bypasses them
in some manner. Phillips and Caldwell are somewhat in favor of the
latter hypothesis, however, because of the obvious relationship between
the small amounts of the limit dextrins, remaining after exhaustive action, and the degree of branching of the substrates. Thus, glucamylase
would be specific for «-1,4-glucosidic bonds. Nothing is known about
the nature of the limit dextrins, which, if the above assumption were
correct, would have to contain all or most of the «-1,6-glucosidic bonds
of the original polysaccharide. No data are available on the action of
this enzyme on dextran or on isomaltose.
Meeuse (227) reported an enzyme in molds (Mucor rouxianus and
several Rhizopus species) that yields glucose directly from starch; it
also contains maltase, and glucose formation may be due to the combined action of ß-amylase and maltase.
Common maltase of various origins has frequently been reported to
liberate glucose from starch. Since maltase is almost always accompanied in nature by α-amylase, the reported action is likely to be due
to the combined effect of the two enzymes; maltase alone is supposedly
an oligosaccharidase and does not attack polysaccharides beyond a
certain degree of polymerization. Maltase is extremely widespread in
both animal and vegetable kingdoms, and its occurrence and specificity
have recently been discussed in detail (228). In many instances, maltase supplements the action of the amylases, e.g., in the digestive tract
of higher animals where it occurs in the intestinal flora and is believed
to be responsible for the formation of glucose.
391
bond, may occur in common with a glucosidase specific for the other
type, and neither enzyme may have been sufficiently purified to permit
of deciding to which class they actually belong. The following classification is, therefore, only a tentative one.
1. a-l,4-Glucosidases
A glucosidase was detected in the mold Rhizopus delemar (224)
and has been isolated in highly purified form, free of a-amylase (225).
It was called glucamylase and has been found to convert corn amylopectin to 95% theoretical glucose; glycogen to 92% glucose; residual ß
dextrins from amylopectin to 89% glucose, and maltose to 100% glucose
(226). Since α-amylase is absent from the preparations of glucamylase,
glucose cannot result from the action of maltase on degradation products of a primary reaction, but must itself be the primary product of
hydrolysis by this enzyme. The authors believe that glucamylase, like
ß-amylase, attacks the nonreducing ends of the glucosidic chains of its
substrate, and they conclude that this enzyme either hydrolyzes «-1,6glucosidic bonds as well as a-l,4-glucosidic linkages or bypasses them
in some manner. Phillips and Caldwell are somewhat in favor of the
latter hypothesis, however, because of the obvious relationship between
the small amounts of the limit dextrins, remaining after exhaustive action, and the degree of branching of the substrates. Thus, glucamylase
would be specific for «-1,4-glucosidic bonds. Nothing is known about
the nature of the limit dextrins, which, if the above assumption were
correct, would have to contain all or most of the «-1,6-glucosidic bonds
of the original polysaccharide. No data are available on the action of
this enzyme on dextran or on isomaltose.
Meeuse (227) reported an enzyme in molds (Mucor rouxianus and
several Rhizopus species) that yields glucose directly from starch; it
also contains maltase, and glucose formation may be due to the combined action of ß-amylase and maltase.
Common maltase of various origins has frequently been reported to
liberate glucose from starch. Since maltase is almost always accompanied in nature by α-amylase, the reported action is likely to be due
to the combined effect of the two enzymes; maltase alone is supposedly
an oligosaccharidase and does not attack polysaccharides beyond a
certain degree of polymerization. Maltase is extremely widespread in
both animal and vegetable kingdoms, and its occurrence and specificity
have recently been discussed in detail (228). In many instances, maltase supplements the action of the amylases, e.g., in the digestive tract
of higher animals where it occurs in the intestinal flora and is believed
to be responsible for the formation of glucose.