This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Miscellaneous (Pharmacology), Subject name: Pharmacology
Which does not act as 2nd messenger? 
Select and explain. 
A. cAMP, B. Guanyl cyclase, C. Diacyl glycerol, D. Inositol triphosphate
B: Guanyl cyclase
Answer: B: Guanyl cyclase 
Explanation: Ans. B. Guanyl cyclase2nd messengers are responsible for conducting and amplifying signals of GPCRs. Following substance act as 2nd messengers:a. cAMP or cGMP causes protein phosphorylationb. IP3- calcium release from ERc. DAG - activates enzymes such as protein kinase C