Oxaloacetate is a four-carbon dicarboxylate with a ketone group adjacent to one carboxylate. It is regenerated in the citric acid cycle rather than consumed as a net reactant on every turn.
Condensation with acetyl-CoA forms citrate; later oxidation of malate regenerates oxaloacetate. Removing oxaloacetate for biosynthesis therefore requires replenishing the cycle's intermediates to sustain flux.[ref]
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