This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
Which of these is not a cofactor for glycogen phosphorylase, an impoant enzyme of the glycogenolysis pathway? 
Select and explain. 
A. Calmodulin, B. c-AMP, C. Protein Kinase A, D. Glycogenin
D: Glycogenin
Answer: D: Glycogenin 
Explanation: Ans: D. Glycogenin(Ref Harper 30/c p 181)Glycogenin:An enzyme involved in glucose conversion to glycogen.Acts as a primer - By polymerizing first few glucose molecules a enzymes take over.Involved in glycogen synthesis pathway rather than glycogenolysis.