In fatty acid beta-oxidation, the entry of long-chain fatty acyl-CoA into the mitochondria requires carnitine shuttle. Which enzyme on the inner mitochondrial membrane regenerates free carnitine inside the mitochondrial matrix?
- A Carnitine palmitoyltransferase I (CPT-I) on the outer mitochondrial membrane
- B Carnitine palmitoyltransferase II (CPT-II) on the inner mitochondrial membrane ✓
- C Carnitine acylcarnitine translocase (CACT)
- D Acyl-CoA synthetase (fatty acyl-CoA ligase)
Explanation
The carnitine shuttle involves: (1) CPT-I (outer membrane, regulatory — inhibited by malonyl-CoA) converts fatty acyl-CoA + carnitine → acylcarnitine + CoA; (2) CACT (inner membrane transporter) exchanges acylcarnitine for free carnitine across the inner membrane; (3) CPT-II (inner membrane, matrix face) converts acylcarnitine + CoA → fatty acyl-CoA + carnitine inside the matrix. CPT-II regenerates free carnitine (returned to cytosol via CACT) and releases fatty acyl-CoA for beta-oxidation. CPT-II deficiency is the most common inherited disorder of fatty acid oxidation, presenting with myoglobinuria after prolonged exercise.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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