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
Second messenger for smooth muscle relaxation mediated by NO is: 
Select and explain. 
A. Ca', B. cAMP, C. cGMP, D. Magnesium
C: cGMP
Answer: C: cGMP 
Explanation: Ans: C. cGMPRef.: Harper 30/e p290, 437)Second messenger for smooth muscle relaxation mediated by NO is cGMP."GTP serves as an allosteric regulator and as an energy source for protein synthesis, and cGMP serves as a second messenger in response to nitric oxide (NO) during relaxation of smooth muscle.