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
The co-factor for glycogen phosphorylase in glycogenolysis is: 
Select and explain. 
A. Thiamine pyrophosphate, B. Pyridoxal phosphate, C. Citrate, D. FAD
B: Pyridoxal phosphate
Answer: B: Pyridoxal phosphate 
Explanation: Glycogen phosphorylase catalyses the rate limiting step in glycogenolysis by catalyzing the phosphorolytic cleavage of glycogen to yield glucose 1-phosphate. Glycogen phosphorylase requires pyridoxal phosphate as its coenzyme.