392
PETER BERNFELD
2. a-lß-Glucosidases
An enzyme of animal origin belonging to this class is the amylo-1,6glucosidase prepared by Cori and Larner (229) from rabbit muscle.
These authors were able to show that amylo-l,6-glucosidase liberates
glucose from glycogen limit dextrins (prepared by exhaustive action of
muscle phosphorylase on glycogen), but not from native glycogen. This
action consists in the hydrolytic splitting of the «-1,6-glucosidic bond
of the branching point after the latter had been exposed by the exhaustive action of phosphorylase. The physiological significance of this
enzyme is easily understood from its ability to supplement phosphorolytic breakdown of glycogen. Thus, a mixture of these two enzymes is
able to digest glycogen to completion, whereas exhaustive action of
phosphorylase alone yields only 36% degradation. In amylopectin the
branching points are hydrolyzed in the same way by amylo-l,6-glucosidase, after being exposed by phosphorylase action. The amount of
free glucose liberated from a branched polysaccharide by the exhaustive action of a mixture of phosphorylase and amylo-l,6-glucosidase
has been found to be directly proportional to the number of branching
points of the polymer. This fact has been applied to end-group determinations of glycogens and amylopectins from various origins, with
the assumption that the number of nonreducing end groups is practically equal to the number of branching points in a polysaccharide of
sufficiently high molecular weight. Amylo-l,6-glucosidase has also been
found to hydrolyze isomaltose, but this reaction appears to be very
slow (229). The study of the histology and cytochemistry of human
skin has resulted in the demonstration of amylo-l,6-glucosidase in stratum spinosum, in growing hair follicles, and in the sebaceous glands
(230).
In plants, an enzyme has been detected which catalyzes the hydrolytic scission of a-l,6-glucosidic linkages in amylopectin (231). It
has been isolated from the potato and the broad bean and is known as
R-enzyme. Its action is strictly that of a "debranching" enzyme and it
appears to have no action on the a-l,4-bonds.
An oligo-l,6-glucosidase that splits a-l,6-glucosidic bonds in low
molecular weight dextrins only and is different from R-enzyme has
been found in intestinal mucosa (232).
3. Unspecific a-Glucosidases
In 1940, a glucosidase from yeast was reported by Meyer and Bernfeld (233). This enzyme has been found to split the terminal «-1,6glucosidic bonds of limit dextrins prepared by exhaustive degradation
PETER BERNFELD
2. a-lß-Glucosidases
An enzyme of animal origin belonging to this class is the amylo-1,6glucosidase prepared by Cori and Larner (229) from rabbit muscle.
These authors were able to show that amylo-l,6-glucosidase liberates
glucose from glycogen limit dextrins (prepared by exhaustive action of
muscle phosphorylase on glycogen), but not from native glycogen. This
action consists in the hydrolytic splitting of the «-1,6-glucosidic bond
of the branching point after the latter had been exposed by the exhaustive action of phosphorylase. The physiological significance of this
enzyme is easily understood from its ability to supplement phosphorolytic breakdown of glycogen. Thus, a mixture of these two enzymes is
able to digest glycogen to completion, whereas exhaustive action of
phosphorylase alone yields only 36% degradation. In amylopectin the
branching points are hydrolyzed in the same way by amylo-l,6-glucosidase, after being exposed by phosphorylase action. The amount of
free glucose liberated from a branched polysaccharide by the exhaustive action of a mixture of phosphorylase and amylo-l,6-glucosidase
has been found to be directly proportional to the number of branching
points of the polymer. This fact has been applied to end-group determinations of glycogens and amylopectins from various origins, with
the assumption that the number of nonreducing end groups is practically equal to the number of branching points in a polysaccharide of
sufficiently high molecular weight. Amylo-l,6-glucosidase has also been
found to hydrolyze isomaltose, but this reaction appears to be very
slow (229). The study of the histology and cytochemistry of human
skin has resulted in the demonstration of amylo-l,6-glucosidase in stratum spinosum, in growing hair follicles, and in the sebaceous glands
(230).
In plants, an enzyme has been detected which catalyzes the hydrolytic scission of a-l,6-glucosidic linkages in amylopectin (231). It
has been isolated from the potato and the broad bean and is known as
R-enzyme. Its action is strictly that of a "debranching" enzyme and it
appears to have no action on the a-l,4-bonds.
An oligo-l,6-glucosidase that splits a-l,6-glucosidic bonds in low
molecular weight dextrins only and is different from R-enzyme has
been found in intestinal mucosa (232).
3. Unspecific a-Glucosidases
In 1940, a glucosidase from yeast was reported by Meyer and Bernfeld (233). This enzyme has been found to split the terminal «-1,6glucosidic bonds of limit dextrins prepared by exhaustive degradation