This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of carbohydrate, Subject name: Biochemistry
Enzymes not used in glycogen metabolism 
Select and explain. 
A. Glycogen phosphorylase B, B. Glycogen synthase I, C. Glycogen synthase C, D. Glycogen synthase D
C: Glycogen synthase C
Answer: C: Glycogen synthase C 
Explanation: The liver phosphorylase-b is the inactive form. It becomes active on phosphorylation. The active form is phosphorylase-a.Glycogen synthase exists in two distinct forms that can be interconveed by the action of specific enzymes; active dephosphorylated glycogen synthase(glucose-6-p-independent) and less active, phosphorylated glycogen synthase D(glucose-6-p-dependent.Ref: DM Vasudevan, page no: 127