Protein kinase A (PKA) is a tetrameric enzyme. What is its subunit composition in the inactive state?
- A Four catalytic subunits (C4)
- B One regulatory and one catalytic subunit (R1C1)
- C Two regulatory and two catalytic subunits (R2C2) ✓
- D Two regulatory and four catalytic subunits (R2C4)
Correct answer: C. Two regulatory and two catalytic subunits (R2C2)
Explanation
Inactive PKA exists as a holoenzyme complex of two regulatory (R) subunits and two catalytic (A) subunits (R2A2). Each R subunit contains a pseudosubstrate domain that inhibits the A subunit. When cAMP binds to the R subunits, they dissociate, releasing active A subunits that phosphorylate target proteins. This structure is fundamental to cAMP-mediated signaling.
Reference: Lehninger Principles of Biochemistry, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.