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
Cofactor for glycogen phosphorylase 
Select and explain. 
A. Thiamine pyrophosphate, B. Pyridoxal phosphate, C. Citrate, D. FAD
B: Pyridoxal phosphate
Answer: B: Pyridoxal phosphate 
Explanation: Pyridoxal phosphate is an essential cofactor for glycogen phosphorylase.