What role does oxaloacetate play in the TCA cycle?

Two of the TCA cycle intermediates, α-ketoglutarate and oxaloacetate serve as precursor metabolites for the biosyntheses of amino acids and nucleotides. There is no net synthesis of these two organic acids in the TCA cycle, and their removal for other cellular functions must be compensated for by other means.

How does oxaloacetate turn into citrate?

The citric acid cycle: In the citric acid cycle, the acetyl group from acetyl CoA is attached to a four-carbon oxaloacetate molecule to form a six-carbon citrate molecule. Through a series of steps, citrate is oxidized, releasing two carbon dioxide molecules for each acetyl group fed into the cycle.

How is oxaloacetate regulated?

The regulation of the supply of oxaloacetate (OAA) for mitochondrial metabolism via phosphoenolpyruvate carboxylase (PEPC) by metabolites is studied in barley (Hordeum vulgare L.) leaf protoplasts in light or darkness as well as under photorespiratory or non-photorespiratory conditions.

Why is oxaloacetate important?

Oxaloacetate, an intermediate in the tricarboxylic acid cycle, plays important roles in regulating mitochondrial function, gluconeogenesis, the urea cycle, and amino acid syntheses.

Can oxaloacetate be converted to aspartate?

Oxaloacetate is then transformed into aspartate (since oxaloacetate cannot be transported into the cytosol) by mitochondrial aspartate aminotransferase. Since aspartate is an amino acid, an amino radical needs to be added to the oxaloacetate.

How is oxaloacetate produced?

A pyruvate molecule is carboxylated by a pyruvate carboxylase enzyme, activated by a molecule each of ATP and water. This reaction results in the formation of oxaloacetate. NADH reduces oxaloacetate to malate. Then oxaloacetate remains in the cytosol, where the rest of reactions will take place.

How is oxaloacetate transported to the cytoplasm?

To complete the shuttle, oxaloacetate must be transported from the matrix to the cytoplasm but there is no such transport system. Instead, oxaloacetate is first converted to aspartate by aspartate aminotransferase (Chapter 17) and then transported out of the mitochondria via the glutamate-aspartate translocase.