Food Chemistry and Fish in Nutrition

6.2.2.4. Action of glycogen synthase

By the action of the enzyme glycogen synthase, the C1 of the activated glucose of UDPGlc forms a glycosidic bond with the C4 of a terminal glucose residue of glycogen, liberating uridine diphosphate (UDP).

Glycogen synthase

UDPGlc + Glycogen primer( n ) → Glycogen(n+1)

A preexisting glycogen molecule, or “glycogen primer”, must be present to initiate this reaction. Further glucose residues are attached in the 1-4 position to make a short chain that is acted upon by glycogen synthase.

The addition of a glucose residue to a preexisting glycogen chain, or “primer,” occurs at the nonreducing, outer end of the molecule so that the “branches” of the glycogen “tree” become elongated as successive α1-4 linkages are formed.