Question

Free palmitate is activated to its coenzyme A derivative (palmitoyl-CoA) in the cytosol before it can be oxidized in the mitochondrion. If palmitate and [14C]coenzyme A are added to a liver homogenate, palmitoyl-CoA isolated from the cytosolic fraction is radioactive, but that isolated from the mitochondrial fraction is not. Explain.

Answer 1

Answer:

The cytosolic and mitochondrial pools of CoA are  kept separate, and no radioactive CoA from the cytosolic pool enters the mitochondrion.

Explanation:

• Fatty acyl group condensed with CoA in the cytosol are first transferred to carnitine and in this process, CoA is released.
• After this, it is transported into the mitochondrion, where it is again condensed with CoA.
• In this way, the cytosolic and mitochondrial pools of CoA are kept separate, and due to this reason, no radioactive CoA from the cytosolic pool enters the mitochondrion.
• Therefore, according to the given question, the C14 CoA that is added into the liver homogenate along with palmitate shows cytosolic radioactive fraction but not mitochondrial as in the mitochondria a different CoA joins palmitate and not the one containing C14.