This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Glycogen Metabolism and Glycogen Storage, Subject name: Biochemistry
Glycogen phosphorylase requires - 
Select and explain. 
A. Thiamine pyrophosphate, B. Pyridoxal phosphate, C. Citrate, D. FAD
B: Pyridoxal phosphate
Answer: B: Pyridoxal phosphate 
Explanation: Ans. is 4b' i.e., Pvridoxal phosphate o Glycogenolysis occurs primarily by phosphorolytic breaking of a-l,4-glycosidic bonds of glycogen. The key enzyme responsible for glycogenolysis is glycogen phosphorylase which catalyses stepwize phosphorolytic removal of glucose as glucose-1-phosphate, from glycogen.o Pvridoxal phosphate is essential cofactor in this reaction; it is covalently bound to glycogen phosphorylase.