Citrate Synthesis in Intact Rat‐Liver Mitochondria Is Irreversible

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Abstract
Rat liver mitochondria were incubated with [1,5-14C]citrate in the presence of fluorocitrate to block its oxidation in the Krebs cycle. The reaction products were analyzed enzymatically and by anion-exchange chromatography. Incorporation of 14C into acetyl-L-carnitine or ketone bodies via a backward action of citrate synthase [EC 4.1.3.7] was not observed. The optimal rate of citrate synthesis from pyruvate and malate in the presence of fluorocitrate was 15 nmol/mg per min. In the absence of fluorocitrate but in the presence of malonate, citrate was oxidized to succinate at a rate of 4 nmol/mg per min. The synthesis of citrate by intact rat liver mitochondria is an irreversible process. The possible mechanism underlying this phenomenon and the consequence for metabolic regulation are discussed.