Branching enzyme glycogen synthase

It should be noted that the other glycogen biosynthetic enzymes, glycogen synthase and branching enzyme in the E. coli mutant strains were at the same level of activity as observed for the wild-type E. coli B and thus could not account for the greater accumulation observed in the glycogen-excess mutants. 

The proglycogen is extended to produce macroglycogen by action of glycogen synthase and the branching enzyme (Figure 6.18). 

Glycogen phosphorylase and glycogen synthase alone are insufficient to synthesize and degrade glycogen. Synthesis also requires the action of the branching enzyme amylo-(l,4 —> 1,6-transglycosylase,97... 

The first enzymic studies done on the dul mutant were carried out in 1981, and both SSII and starch-branching enzyme Ha (SBEIIa) were found to have reduced activity in the endosperm compared to normal maize endosperm.204 SSII was shown to be different from SSI.173,205 SSII requires a primer for activity, and could not catalyze an unprimed reaction even in the presence of 0.5 M citrate, it also has less affinity for amylopectin than does SSI. However, 0.5 M citrate lowered the Km for amylopectin 17-fold. The activity with glycogen as a primer is one-half that observed with amylopectin. Therefore, glycogen is not as effective as a primer as is amylopectin, which differs from what was observed for starch synthase I. Both maize endosperm SSI and SSII had a Km for ADPGlc of 0.1 mM.196,205... 

Biosynthesis of glycogen requires dephosphorylated (active) glycogen synthase and an enzyme that creates branch points in the growing glycogen molecule, glucosyl-4,6-transferase. 

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