anaplerottorin

Anaplerottorin (anaplerosis) refers to metabolic processes that replenish the intermediates of the tricarboxylic acid (TCA) cycle after they have been drawn off for biosynthetic purposes. The cycle requires a steady supply of intermediates such as oxaloacetate, α-ketoglutarate, succinyl‑CoA, and malate to function in energy production and to support other pathways. When these compounds are diverted for the synthesis of nucleotides, fatty acids, or amino acids, anaplerotic inputs restore the pool of TCA cycle intermediates.

The best characterized anaplerotic route in many tissues is the mitochondrial carboxylation of pyruvate to oxaloacetate by pyruvate carboxylase, using CO2 and ATP. In plants, bacteria, and some mammalian tissues, phosphoenolpyruvate carboxylase can also generate oxaloacetate from phosphoenolpyruvate. Propionyl-CoA carboxylase provides succinyl‑CoA from propionyl‑CoA, linking propionate metabolism to the cycle. Glutaminolysis supplies α‑ketoglutarate via conversion of glutamine and glutamate, another major anaplerotic source. Transaminations and other enzymes can contribute oxaloacetate through aspartate, while malate can be formed from various precursors to feed malate dehydrogenase.

Physiological roles include maintaining TCA cycle flux during biosynthesis, supporting gluconeogenesis in the liver by balancing intermediates, and sustaining energy production in rapidly proliferating cells. Anaplerosis interacts with cataplerosis, the removal of intermediates for biosynthesis, and is regulated by nutrient availability, energy status, and hormonal signals.

Clinical and nutritional relevance appears in metabolic disorders affecting pyruvate carboxylase activity or glutaminolysis, and in conditions where altered anaplerosis contributes to disease progression or adaptation, such as certain cancers and liver metabolism.