1— >6 glycosidic branch point

In contrast, amylopectin contains 1—>6 glycosidic branch points at regular intervals. These result in an open, treelike stracture. Amylopectin is more readily hydrolyzed by amylase, and this results in a mixture of small, branched maltodextrin molecules that are often referred to as limit dextrins. Limit dextrins are further hydrolyzed by maltase. 

The hydrolysis of starch by salivary and pancreatic amylases catalyze random hydrolysis of a(l—>4) glycoside bonds, yielding dextrins, then a mixmre of glucose, maltose, and isomaltose (from the branch points in amylopectin). 

Branches are created by forming glycosidic linkages with both the 4- and 6-hydroxyl groups of the glucose residue at the branch point. The glycogen polymer is very large and contains multiple branches. 

Glycogen is a polymer of D-glucose monomers, linked via a 1-4 glycosidic bonds with al-6 links creating branch points (Figure 6.21). 

Glycogen phosphorylase sequentially cleaves the cx(1 -h>4) glycosidic bonds between the glucosyl residues at the nonreducing ends of the glycogen chains by simple phosphorolysis until four glucosyl units remain on each chain before a branch point (Figure 11.7). [Note ... 

It thus became desirable to understand, first, the basis of this determinism in the creation of glycosidic linkages, and second, the order in which the residues of monosaccharides of the branching points are conjugated. Some work has now been performed that demonstrates that this double problem is linked simultaneously to the specificity of the glycosyltransferases and to the presence of well defined, oligosaccharide structures in the glycan molecule. For example, Roseman s... 

Amylopectin Amylopectin, the insoluble fraction of starch, is also primarily an a-1,4 polymer of glucose. The difference between amylose and amylopectin lies in the branched nature of amylopectin, with a branch point about every 20 to 30 glucose units. Another chain starts at each branch point, connected to the main chain by an a-1,6 glycosidic linkage. A partial structure of amylopectin, including one branch point, is shown in Figure 23-20. 

Figure 11.13. Branch Point in Glycogen. Two chains of glucose molecules joined by a -1,4-glycosidic bonds are linked by an a -1,6-glycosidic bond to create a branch point. Such an a -1,6-glycosidic bond forms at approximately...

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