8. POLYSACCHARIDASES
395
nized during the past ten years, and their investigation has provided
considerable insight into the nature and action of dextranases.
A. MECHANISM OF ACTION
Early experiments (242, 243) with dextranase from cultures of bacteria and molds demonstrated the ability of this enzyme to reduce the
viscosity of dextran solutions and, hence, to act in the general manner
of an α-amylase. Mold dextranase was reported to split the a-1,6 bonds
of dextran at random, and to stop at a degradation of 50-60% isomaltose
(244).
The products of degradation of dextran by dextranase from two
strains of Penicillium funiculosum have been studied by Jeanes et al.
(245). After treatment of dextran with the enzyme from strain 1768,
these authors found among the end products 3.7% glucose, 45$ isomaltose, and 22% isomaltotriose, whereas dextranase from strain 1132
produced slightly different end products, i.e., 11% glucose, 53% isomaltose, and 7% isomaltotriose.
The action of mammalian dextranase was reported, however, to
yield glucose as the sole product of dextran degradation (246, 247),
and Sery and Hehre (248), working with dextranase from intestinal
bacteria, also found glucose as the sole and major product of dextran
breakdown, but observed different pH optima for the liquefying and
saccharifying action of this enzyme. These workers concluded that two
separate enzymes are involved in the biological degradation of dextran,
the action of which would be analogous to that of a- and ß-amylases.
B. OCCURRENCE
Dextranase appears to be quite widely distributed in microorganisms
(molds, bacteria), but its presence in mammalian tissues has equally
been reported. Like amylases and cellulases, dextranase is an extracellular enzyme. A summary of dextrinase occurrences is given in Table
XVII.
C. CONCLUSIONS
Although the types of glucosidic linkages in the starch polysaccharides and in dextran are the same, i.e., a-1,4- and a-l,6-glucosidic bonds,
the enzymes that digest the two groups of polysaccharides are completely different. This implies that the specificity of these enzymes depends not only on the nature of the glucosidic bond, but is governed
also by the type of the adjoining glucosidic bonds and/or by the structure of the whole polysaccharides.
395
nized during the past ten years, and their investigation has provided
considerable insight into the nature and action of dextranases.
A. MECHANISM OF ACTION
Early experiments (242, 243) with dextranase from cultures of bacteria and molds demonstrated the ability of this enzyme to reduce the
viscosity of dextran solutions and, hence, to act in the general manner
of an α-amylase. Mold dextranase was reported to split the a-1,6 bonds
of dextran at random, and to stop at a degradation of 50-60% isomaltose
(244).
The products of degradation of dextran by dextranase from two
strains of Penicillium funiculosum have been studied by Jeanes et al.
(245). After treatment of dextran with the enzyme from strain 1768,
these authors found among the end products 3.7% glucose, 45$ isomaltose, and 22% isomaltotriose, whereas dextranase from strain 1132
produced slightly different end products, i.e., 11% glucose, 53% isomaltose, and 7% isomaltotriose.
The action of mammalian dextranase was reported, however, to
yield glucose as the sole product of dextran degradation (246, 247),
and Sery and Hehre (248), working with dextranase from intestinal
bacteria, also found glucose as the sole and major product of dextran
breakdown, but observed different pH optima for the liquefying and
saccharifying action of this enzyme. These workers concluded that two
separate enzymes are involved in the biological degradation of dextran,
the action of which would be analogous to that of a- and ß-amylases.
B. OCCURRENCE
Dextranase appears to be quite widely distributed in microorganisms
(molds, bacteria), but its presence in mammalian tissues has equally
been reported. Like amylases and cellulases, dextranase is an extracellular enzyme. A summary of dextrinase occurrences is given in Table
XVII.
C. CONCLUSIONS
Although the types of glucosidic linkages in the starch polysaccharides and in dextran are the same, i.e., a-1,4- and a-l,6-glucosidic bonds,
the enzymes that digest the two groups of polysaccharides are completely different. This implies that the specificity of these enzymes depends not only on the nature of the glucosidic bond, but is governed
also by the type of the adjoining glucosidic bonds and/or by the structure of the whole polysaccharides.