1,4-a-glucan branching enzyme

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. 

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... 

Reaction (7) is catalyzed by starch synthases (EC 2.4.1.21 ADP-Glc 1,4-a-D-glucan 4-a-glucosyltransferase), the same reaction as the one catalyzed by the bacterial glycogen synthase (Reaction (2)). Here a different reaction number is given to stress that the final products of starch, amylose, and amylopectin, are different in structure. Isozymic forms of plant starch synthases z.i i-is,65-69 of branching enzymes 4-i 6,65,66,70-76 reported. 

The action of a bacterial starch-branching enzyme elaborated by Bacillus stearothermophilus with amylose also produced a nonreducing cyclic a-1 4-D-glucan (cycloamylose) [68]. The product in this reaction had one a-1 6 glyco-... 

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