Amylopectin beta-amylase action

By use of a debranching enzyme, isoamylase or pullulanase, the a-D-(l — 6)-linkages in amylopectin are broken, thus opening up to beta-amylase action those parts of the amylopectin molecule that are otherwise resistant.14 In this way, syrups of very high maltose content can be made.19... 

The data19 summarized in Figure 1 show that the extent of the hydrolysis of soluble potato starch by barley beta amylase reaches a limit which is independent of the concentration of the amylase. The data are typical of the action of beta amylases on unfractionated starches, when the hydrolyses are carried out at or near pH 4.5.1 3 6 19 20 Under these conditions, the hydrolysis of unfractionated starches usually ceases when 60 to 64% of the maltose theoretically obtainable from the substrate has been formed. The exact value of the limit obviously will depend upon the concentration of amylopectin in the starch and upon its structure. 

Although all amylose molecules were once considered to be linear, many amylose molecules cannot be completely hydrolyzed by (3-amylase. With a concurrent or mixed action of pullulanase and beta-amylase, however, amylose can be completely hydrolyzed to maltose.150,151 These results rule out the theory that the incomplete hydrolysis of amylose by (3-amylase is a result of retrogradation, i.e. junction zone formation. It is now clear that the incomplete hydrolysis of an amylose preparation by (3-amylase is due to branching of some molecules. The (3-amylolysis limit of amylose varies from 72% to 95%152,153 compared with 55-61% for amylopectin. Amylose of most cereal starches, such as maize,154 rice,155,156 wheat157 and barley,158 give >80% (3-amylolysis... 

Fig. 11.—Successive Actions of Phosphorylase, beta-Amylase, Isoamylase, and befa-Amylase on the Meyer Model of Amylopectin and Glycogen. [The symbolism is basically that of Fig. 9, modified to show the action of the various enzymes as follows - - - removed by pho horylase and heto>amylase , branch points hydrolyzed by isoamylase and-, immune to beta amy]ase after isoamylase action.]...

At the concentration used, debranching of amylopectin and its beta-limit dextrin was incomplete, and there was no action on glycogen. First-stage, alpha-amylase limit-dextrins, those containing side chains of... 

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