Question

In Protein Kinase A, the letter ‘A’ refers to

• A. cGMP
• B. cAMP
• C. ATP
• D. GTP

Hint:

Similarly, in Protein Kinase G (PKG), the 'G' refers to cGMP dependency, and in Protein Kinase C (PKC), the 'C' refers to Calcium (\(Ca^{2+}\)) dependency.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Protein kinases are enzymes that regulate cellular processes by phosphorylating specific target proteins.
Many of these kinases are activated by intracellular second messengers.

Step 2: Detailed Explanation:
Protein Kinase A (PKA) is a multi-subunit enzyme consisting of two regulatory (R) subunits and two catalytic (C) subunits, forming an inactive \(R_2C_2\) tetramer.
PKA is activated by the intracellular second messenger cyclic adenosine monophosphate (cAMP), which is produced from ATP by the enzyme adenylyl cyclase.
When intracellular cAMP levels rise, four molecules of cAMP bind to the regulatory subunits of the PKA tetramer (two per subunit).
This binding induces a conformational change that triggers the dissociation of the active catalytic subunits from the regulatory dimer.
Once released, the free catalytic subunits phosphorylate target serine and threonine residues on specific cellular proteins.
Because this enzyme is dependent on cyclic AMP for its activation, the 'A' in Protein Kinase A stands for cAMP.

Step 3: Final Answer:
In Protein Kinase A, the letter 'A' refers to cAMP.