Question

The second messenger cAMP is inactivated by

• A. Adenyl cyclase
• B. Guanylyl cyclase
• C. Phospholipase C
• D. Phosphodiesterase

Hint:

cAMP Signaling Dynamics:
Synthesis = Adenylyl Cyclase (ATP $\rightarrow$ cAMP).
Inactivation = PHOSPHODIESTERASE PDE (cAMP $\rightarrow$ 5'-AMP).

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Intracellular cyclic nucleotide termination: cyclic nucleotide phosphodiesterases hydrolyze the 3',5'-phosphodiester bond of cyclic AMP into inactive 5'-AMP.
Key Formula or Approach:
\[ \text{cAMP} + \text{H}_2\text{O} \xrightarrow{\text{Phosphodiesterase (PDE)}} 5'\text{-AMP (Inactive)} \]

Step 2: Detailed Explanation:
In intracellular second messenger signal transduction:
1. cAMP Synthesis: Adenylyl cyclase synthesizes cyclic adenosine 3',5'-monophosphate (cAMP) from ATP.
2. cAMP Inactivation: Phosphodiesterase (PDE) enzymes hydrolyze the internal cyclic $3',5'$-phosphodiester bond of cAMP, converting it into inactive linear $5'$-AMP, thereby terminating protein kinase A (PKA) activation.
- PDE inhibitors (e.g., Methylxanthines like theophylline, caffeine, and pimobendan) block this degradation, prolonging intracellular cAMP signaling.

Step 3: Final Answer:
Thus, cAMP is inactivated by Phosphodiesterase, corresponding to option (D).