In liver, which of the following inhibitory effects is the key regulatory event that ensures newly synthesized palmitoyl-CoA is not immediately oxidized?

A. Acyl-CoA synthetase by malonyl-CoA

B. Carnitine-acylcarnitine translocase (CAT) by palmitoyl-CoA

C. Carnitine-palmitoyl transferase-I (CPT-I) by malonyl-CoA

D. CPT-I by palmitoylcarnitine

E. Carnitine-palmitoyl transferase-II (CPT-II) by acetyl-CoA

Answer: C. Carnitine-palmitoyl transferase-I (CPT-I) by malonyl-CoA.

Explanation: Carnitine-palmitoyl transferase-I (CPT-I) is a mitochondrial protein that mediates transport of long-chain fatty acids from cytoplasm to mitochondria, bond to carnitine (amine derived from lysine and methionine). This transport into the mitochondria is for the fatty acid can be oxidized, to produce energy. After food intake, glucose levels rise and the concentration of acetyl-CoA rises too and Malonyl-CoA is synthetize and inhibite the CPT-I transport. High levels of Malonyl-CoA mean that energy are avaible and fatty acids can be made, hence, not oxidize.