ossalacetato

Oxaloacetate, sometimes written ossalacetato, is a four‑carbon dicarboxylic acid that bears a keto group and serves as a central metabolite in cellular metabolism. It is primarily formed in the mitochondria by the oxidation of malate and participates in multiple pathways, including transfer between subcellular compartments via shuttle systems such as the malate–aspartate shuttle. At physiological pH, oxaloacetate exists mainly as negatively charged derivatives, which influences its transport and compartmentalization.

In metabolism, oxaloacetate has key roles in both the citric acid cycle and gluconeogenesis. In the cycle, it condenses with acetyl‑CoA to form citrate, initiating periodic flux through the cycle. It can be replenished by pyruvate carboxylase through carboxylation of pyruvate, providing anaplerotic input to maintain cycle intermediates. For glucose production, oxaloacetate is converted to phosphoenolpyruvate by phosphoenolpyruvate carboxykinase, a pivotal step in gluconeogenesis that generates substrates for endogenous glucose synthesis. Oxaloacetate also participates in amino acid metabolism via transamination: oxaloacetate plus glutamate yields aspartate and alpha‑ketoglutarate, linking the TCA cycle with amino acid biosynthesis and nitrogen metabolism.

Physiological significance and variation: oxaloacetate serves as a hub linking energy production, carbon skeleton provisioning, and amino acid metabolism. In plants, oxaloacetate participates in anaplerotic and C4/CAM pathways, where it is involved in malate production for carbon fixation. Dysregulation of oxaloacetate production or its flux through these pathways can impact energy balance and metabolic homeostasis in cells.