Fatty acid oxidation occurs in the mitochondrial matrix. However, long-chain fatty acyl-CoA molecules cannot cross the inner membrane to enter the matrix. The carnitine shuttle system transfers the acyl group from CoA to carnitine, which can enter the mitochondrial matrix. Label the enzymes and compounds of the carnitine shuttle system. Note the use of abbreviations: IMS for intermembrane space, CPT1 for carnitine palmitoyl transferase I, and CPT2 for mitochondrial carnitine palmitoyl transferase II. Anwwer Bank R-C-SCOA CH HSCO acyl-carnitine RG- CH)N-CH-CH-CH2-C00 CHIN-CH-CH-CH-COD transporter CPT2 cytosol and IMS Carnitine CPTI mitochondrial matrix R-c-o CH3-N-CH, C D CDU -CH-CH-C00 HSCA SCOA hep
The Correct Answer and Explanation is :
Carnitine Shuttle System Components and Enzymes
- CPT1 (Carnitine Palmitoyl Transferase I):
- Located in the outer mitochondrial membrane.
- Function: Transfers the fatty acyl group from CoA to carnitine, forming acyl-carnitine.
- Reactants: Fatty acyl-CoA + Carnitine.
- Products: CoA + Acyl-carnitine.
- Translocase (Transporter):
- Located in the inner mitochondrial membrane.
- Function: Facilitates the exchange of acyl-carnitine into the matrix and free carnitine back into the intermembrane space (IMS).
- CPT2 (Carnitine Palmitoyl Transferase II):
- Located in the inner mitochondrial membrane, matrix-facing side.
- Function: Transfers the fatty acyl group back from carnitine to CoA, regenerating fatty acyl-CoA in the matrix for β-oxidation.
- Reactants: Acyl-carnitine + CoA.
- Products: Carnitine + Fatty acyl-CoA.
Key Compounds
- Carnitine: Molecule that shuttles the fatty acyl group across the inner membrane.
- Acyl-carnitine: Intermediate that crosses the inner membrane via the translocase.
- Fatty acyl-CoA: Activated fatty acid for β-oxidation.
- CoA: Coenzyme A, released in the IMS during the reaction with CPT1 and regenerated in the matrix via CPT2.
Explanation (300 Words)
Fatty acid oxidation occurs in the mitochondrial matrix, but long-chain fatty acyl-CoA molecules cannot cross the impermeable inner mitochondrial membrane. The carnitine shuttle system resolves this by transferring the fatty acyl group from CoA to carnitine, forming acyl-carnitine, which can traverse the membrane.
The process begins in the cytosol and intermembrane space (IMS) with CPT1, which catalyzes the transfer of the fatty acyl group from CoA to carnitine. This forms acyl-carnitine, a compound capable of passing through the inner membrane via a translocase, which exchanges acyl-carnitine for free carnitine.
Inside the mitochondrial matrix, CPT2 transfers the fatty acyl group back to CoA, regenerating fatty acyl-CoA and free carnitine. The fatty acyl-CoA then undergoes β-oxidation to produce acetyl-CoA, NADH, and FADH2 for ATP generation. Meanwhile, free carnitine is transported back to the IMS by the translocase, completing the cycle.
This shuttle system ensures that fatty acid metabolism is compartmentalized, with activation in the cytosol and degradation in the mitochondrial matrix, optimizing energy production while maintaining separation of metabolic processes.