1,4-a-glucan, branching

Table 4.6.14 Enzyme activities (1,4-a-glucan branching enzyme) in liver, muscle, and fibroblasts... 

It is noteworthy in passing that the branching enzyme involved in the synthesis of potato amylopectin acts on a complex of two chains, each containing 40 D-glucosyl residues. Branching is suggested to take place between two adjacent chains of 1,4-a-glucan that are covalently attached to the protein primer. 

Dextran sulfate A chemically sulfated (1 —> 4)-/3-D-, (1 - 3)-a-D-branched glucan polymer... 

Dextran is a structurally heterogeneous glucan containing linear and branched sequences with a preponderance of 1,6-a-D (isomaltose) and a smaller percentage of 1,2-a, 1,3-a, and 1,4-a-n linkages. This heterogeneity results in easy dispersion in hot and cold water. Insolubility is associated with 1,3-a linkages (Sidebotham, 1974). 

Figure 10-5 Diagrammatic Representation of Amylopectin Structure. Lines represent a-D-glucan chains linked by 1,4-bonds. The branch points are 1,6-a glucosidic bonds. Source From J.J. Marshall, Starch Degrading Enzymes, Old and New, Starke, Vol. 27, pp. 377-383, 1975.

Borovsky, D., Smith, E. E., and Whelan, W. J. 1975. Purification and properties of potato 1,4-a-D-glucan 1,4-a-D-glucan, 6-a-(l,4-a-D-glucano)-transferase. Evidence a dual catalytic function in amylose branching enzyme. Eur. J. Biochem. 59, 615-625. 

Synthesis of the 1,6-a-D-glucose bonds in amylopectin is catalyzed by a branching enzyme [E.C. 2.4.1.18 1,4-a-D-glucan 6-a-(l,4-a-glucano)-transferase reaction 3]. Amylopectin contains longer chains (about 20-24 glucosyl units) and has less... 

Most starches are composed of two kinds of polysaccharides, a linear o -(1 4) linked glucan, called amylose, and an o -(1 4) linked glucan with 4.2 to 5.9% a-(l 6) branch linkages, called amylopectin. See O Fig, 1 for the chemical structure of a segment of amylose and a segment of amylopectin and O Table 1 for the percent branching in amylopectin for several different starches. 

ADP-glucose - - a-l,4-glucan —> a- 1,4-glucosyl-glucan - - ADP a-1,4-oligosaccharide a-1,4-glucan o -l,4-a-l,6 branched glucan... 

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