Cyclic AMP increase the rate of glycogenolysis by: (A) Promoting the formation of phosphorylase, (B) Acting as a cofactor for glycogen phosphorylase, (C) Furnishing phosphate for the phosphorylysis of glycogen, (D) Acting as a precursor of 5' AMP which is a cofactor for glycogen phosphorylase
Answer is A. The roles of cAMP and inorganic phosphate (Pi) in the regulation of muscle glycogenolysis during exercise have been investigated in humans using the needle biopsy technique. The fraction of phosphorylase a in resting muscle was as a mean 23%, but the rate of glycogenolysis was extremely low. Epinephrine infusion increased cAMP in muscle by 3-fold and transformed 80% of phosphorylase to the form