The Key Role of Anaplerosis and Cataplerosis for Citric Acid Cycle Function

Tricarboxylic acid cycle phosphoenolpyruvate carboxykinase phosphoenolpyruvate The oxidation of acetyl-CoA to CO2by the TCA1 cycle is the central process in energy metabolism. However, the TCA cycle also functions in biosynthetic pathways in which intermediates leave the cycle to be converted primarily to glucose, fatty acids, or non-essential amino acids. If TCA cycle anions are removed from the cycle they must be replaced to permit its continued function. This process is termed anaplerosis. Pyruvate carboxylase, which generates oxalacetate directly in the mitochondria, is the major anaplerotic enzyme. Conversely, 4- and 5-carbon intermediates enter the TCA cycle during the catabolism of amino acids. Because…