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 coenzyme associated is? 
Select and explain. 
A. Thiamine pyrophosphate, B. Tetrahydrofolate, C. Flavin mononuleotide, D. Pyridoxal phosphate
D: Pyridoxal phosphate
Answer: D: Pyridoxal phosphate 
Explanation: ANSWER: (D) Pyridoxal phosphateREF: Lehninger Principles of Biochemistry 4th edition page 562Pyridoxal phosphate is an essential cofactor in the glycogen phosphorylase reaction; itsphosphate group acts as a general acid catalyst, promoting attack by Pi on the glycosidic bond. (This is an unusual role for this cofactor; its more typical role is as a cofactor in amino acid metabolism)Flavin mononucleotide (FMN), or riboflavin-5'-phosphate, is a biomolecule produced from riboflavin (vitamin B2) by the enzyme riboflavin kinase and functions as prosthetic group of various oxidoreductases including NADH dehydrogenase as well as cofactor in biological blue- light photo receptors