The process of Beta-oxidation and fatty acid synthesis are regulated in such a manner that neither process is active at the same time. Which of the following enzymes required for fatty acid synthesis is paired with the correct activator?

a) Carnitine palmitoyl transferase 1 (CPT1); malonyl CoA

b) Hormone sensitive lipase; free fatty acids

c) Acetyl COA carboxylase; citrate

d) Citrate synthesis; acetyl COA

c) Acetyl COA carboxylase; citrate

Explanation:

Citrate serves as an allosteric activator for fatty acid synthesis and diverts the cellular metabolism from the consumption of metabolic fuel to the storage of fuel as fatty acids. When the concentrations of mitochondrial acetyl-CoA and ATP increase, citrate is transported out of mitochondria into the cytosol. In the cytosol, citrate serves as the precursor of cytosolic acetyl-CoA and an allosteric activator of acetyl-CoA carboxylase.

The enzyme Acetyl-CoA carboxylase has three functional regions. Its biotin carboxylase activates CO2 and its transcarboxylase transfers activated CO2 from biotin to acetyl-CoA to produce malonyl-CoA.