Anaplerotic reactions

The TCA cycle is a hub of metabolism, with central importance in both energy production and biosynthesis. Therefore, it is crucial for the cell to regulate concentrations of TCA cycle metabolites in the mitochondria. Anaplerotic flux must balance cataplerotic flux in order to retain homeostasis of cellular metabolism.

Reactions of anaplerotic metabolism

There are five major reactions classed as anaplerotic, and it is estimated that the production of oxaloacetate from pyruvate has the most physiologic importance.

The malate is created by PEP carboxylase and malate dehydrogenase in the cytosol. Malate, in the mitochondrial matrix, can be used to make pyruvate (catalyzed by malic enzyme) or oxaloacetic acid, both of which can enter the citric acid cycle.

Glutamine can also be used to produce oxaloacetate during anaplerotic reactions in various cell types through "glutaminolysis," which is also seen in many c-Myc transformed cells. Anaplerotic enzymes mediate an alternative pathway to insulin secretion by aiding the production of cytosolic signal molecules. Pancreatic β-cells, which regulate blood glucose level by secreting insulin, contain high a mounts of pyruvate carboxylase. A decrease in insulin secretion and anaplerotic activity has been found in β-cells that do not have hypoxia-inducible factor-1 beta.