Which statement correctly describes the subcellular locations of acyl transferase and CPT II?

• A. Acyl transferase in the mitochondria; CPT II in the cytosol
• B. Acyl transferase in the cytosol; CPT II in the mitochondria
• C. Both in mitochondria
• D. Both in cytosol

Answer: (B)

Activation of long-chain fatty acids happens in the cytosol by acyl-CoA synthetases, which convert free fatty acids to acyl-CoA so they can be transported into mitochondria. The carnitine shuttle then moves the acyl group into the mitochondrial matrix, where CPT II re-forms acyl-CoA from acyl-carnitine for the beta-oxidation enzymes to act on. Therefore, the acyl transferase is located in the cytosol, while CPT II is located in the mitochondria (on the inner membrane/matrix side). This arrangement allows fatty acids to be activated outside the mitochondrion and then efficiently processed inside.