Branched polysaccharide glycogen

Figure 7.18 A simplified representation of the branched polysaccharide glycogen (branches every 8-12 glucose units). Amylopectin is much less densely branched (branches every 24—30 glucose units). Each small hexagon represents a single glucose unit.

In amylopectin and glycogen p =p is the branching probability, which does not depend on the molar mass of the branched polysaccharides. 

Glycogen is the main storage polysaccharide of animal cells. Like amylopectin, glycogen is a polymer of (a 1—>4)-linked subunits of glucose, with (a 1 >6)-linked branches, but glycogen is more extensively branched (on average, every 8 to 12 residues) and more compact than starch. Glycogen is especially abundant in the liver,... 

Concanavalin A is an antibody-like protein isolated from the jack bean. 82 It was shown to form a precipitate with glycogen and with yeast mannan, and was later also used to differentiate between glycogen-like polysaccharides from various sources.283 284 It has now been shown that concanavalin A forms a precipitate only with branched polysaccharides which contain terminal, nonreducing a-D-glucopyranosyl or a-D-manno-pyranosyl groups.18 The combining sites of the protein appear to be directed against the 2-deoxy-a-D-aratano-hexopyranosyl system.2 ... 

In this article, the term glycogen is used to describe a group of highly branched polysaccharides, isolated from animals or microorganisms, which conform to the following criteria. 

For the synthesis of glycogen-type polysaccharides from a-n-glucopyran-osyl phosphate, two enzymes are required. Phosphorylases, in presence of a suitable primer, synthesize linear chains of -( —> 4)-linked n-glucose residues these are then converted into a branched polysaccharide by a branching enzyme. ... 

The conversion of sucrose into a branched polysaccharide of the amylo-pectin-glycogen type by a bacterial-enzyme system was discovered by Hehre and his coworkers. Enzyme action involves the synthesis of polymeric chains of (1— 4)-linked a-D-glucose residues by a transglucosylase named amylosucrase, followed by the action of a branching enzyme. 

The formation of a branched polysaccharide, similar to glycogen, which is present in certain plants, especially waxy maize, has not yet been clarified however, it could be explained by interaction with starch phosphorylase or starch synthetase, causing branching. Neither the mechanisms for the separate formation of the linear and branched amylopectin components, nor the proportions of each in various plants, are known at present. These problems are undoubtedly a matter of genetic determinants that are awaiting future elucidation. 

Early structural studies (63) on starch indicated an a-(1 4)-linked glucan with some a-(1 6) branches, but it was not realized until considerably later (64) that starch is composed of two polymers, a fully linear component termed amylose and a branched component in which a-(1 6) branches lead to a tree-like structure (amylopectin). The chemistry and technology of starch is detailed in two major treatises (65,66). The animal storage polysaccharide glycogen has a structure similar to that of amylopectin, but is more highly branched (67). 

Glycogen A huge branched polysaccharide of glucose, a store of energy in humans and animals. Glycoside A sugar acetal, linking monosaccharides. 

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