What is the cost in ATP for fatty acid synthesis in eukaryotes when transferring acetyl-CoA into the cytosol?

In eukaryotic cells, fatty acid synthesis occurs in the cytosol, while acetyl-CoA is generated in the mitochondria during the breakdown of glucose via glycolysis and the citric acid cycle. To facilitate the transport of acetyl-CoA from the mitochondria to the cytosol, it must first form citrate using the enzyme citrate synthase. Once citrate is transported into the cytosol, it is then converted back to acetyl-CoA and oxaloacetate by the enzyme ATP-citrate lyase.

The cost of this process involves the hydrolysis of ATP during the conversion of citrate back to acetyl-CoA. Specifically, the hydrolysis of 1 molecule of ATP is required to regenerate acetyl-CoA from citrate. However, since the conversion of citrate to oxaloacetate and the release of acetyl-CoA also involves the utilization of ATP equivalents in the form of nucleotide triphosphates during these reactions, the overall cost is equivalent to using 2 ATP.

Thus, across the entire transfer and conversion process, the cost in ATP for transferring acetyl-CoA into the cytosol for fatty acid synthesis is considered to be 2 ATP molecules. This highlights the energetic expense associated with