Enzymatic Debranching of Starch-type Polysaccharides

Abstract

The action patterns of enzymes, which are able to hydrolyze α-1, 6 glucosidic linkages at the branching points in starch-type polysaccharides, are reviewed. The enzyme of this type found first was the yeast isoamylase, which was proved to split the branching points in amylopectin, glycogen, and dextrins. Similar enzymes were found later in higher plants and bacteria. However, actions of all these enzymes were not identical, as every enzyme had its own substrate specificity. There are several other enzymes which can act on the branching points in low molecular weight dextrins but not in native amylopectin or glycogen. An enzyme, amylo-1, 6-glucosid ase found in higher animals, is specific to phosphorylase limit dextrin. Its action mechanism is not fully established, so far the fact known is the involvement of a transglucosylation in the breakdown of this limit dextrin. In addition to enzymes mentioned above, glucoamylases of microbial origin are able to split α-1, 6- as well as α-1, 4-glucosidic linkages in branched polysaccharides, to attain complete degradation into glucose. Differences in the actions of these enzymes were discussed, enzymes were classified according to their specificity, and summarized in a table.