What does the excess citrate released from the citric acid cycle stimulate in the liver?

The excess citrate released from the citric acid cycle plays a crucial role in metabolic regulation, particularly in the liver. When the energy demands of the cell are met and there is a surplus of acetyl-CoA, citrate accumulates. This excess citrate is transported out of the mitochondria into the cytosol, where it serves as a key signal for anabolic processes.

One of the primary functions of citrate in the cytosol is to stimulate fatty acid synthesis. This occurs because citrate activates acetyl-CoA carboxylase, the enzyme that converts acetyl-CoA into malonyl-CoA, a critical precursor in the fatty acid biosynthetic pathway. As a result, the presence of excessive citrate indicates that there is not only sufficient energy but also building blocks available for synthesizing fatty acids, allowing the cell to convert surplus energy into stored fat.

Citrate’s role in stimulating fatty acid synthesis illustrates its function as a metabolic signal, aligning energy storage with cellular needs. This response is particularly important in the liver, where lipid metabolism is a central aspect of overall energy balance.