Oksaloetaatti

Oksaloetaatti, or oxaloacetic acid (oxaloacetate), is a four-carbon dicarboxylic acid with a keto group, often depicted as HOOC-CH2-CO-COOH. It is a central metabolite in cellular energy metabolism.

In mitochondria, oxaloetaatti is produced from pyruvate by the enzyme pyruvate carboxylase, an anaplerotic reaction that replenishes TCA cycle intermediates and provides substrate for gluconeogenesis. This process requires bicarbonate and ATP. Because oxaloetaatti cannot freely cross the inner mitochondrial membrane, it is typically converted to malate or aspartate for transport; once outside the mitochondrion, it is reconverted to oxaloetaatti.

Within the tricarboxylic acid cycle, oxaloetaatti condenses with acetyl-CoA to form citrate, catalyzed by citrate synthase, thereby regenerating oxaloetaatti for continued operation of the cycle. Oxaloetaatti also participates in amino acid metabolism through transamination to form aspartate, a reaction catalyzed by aspartate aminotransferase.

In gluconeogenesis, oxaloetaatti is a key substrate that can be converted to phosphoenolpyruvate (PEP) by phosphoenolpyruvate carboxykinase (PEPCK) in a rate-limiting step, enabling the synthesis of glucose from non-carbohydrate precursors. The interconversion between oxaloetaatti, malate, and aspartate supports the transport and redistribution of carbon skeletons between cellular compartments.

Physiological regulation involves activation of pyruvate carboxylase by acetyl-CoA and the cellular redox state influencing malate dehydrogenase steps. Oxaloetaatti thus links the TCA cycle, gluconeogenesis, and amino acid metabolism, making it a pivotal intermediate in energy and carbon metabolism.