title: Citrate synthesis in intact rat-liver mitochondria is irreversible.
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 analysed enzymatically and by anion-exchange chromatography. Incorporation of 14C into acetyl-L-carnitine or ketone bodies via a backward action of citrate synthase was not observed. The optimal rate of citrate synthesis from pyruvate and malate in the presence of fluorocitrate was 15 nmol . mg-1 min-1. In the absence of fluorocitrate, but in the presence of malonate, citrate was oxidized to succinate at a rate of 4 nmol . mg-1 . min-1. We conclude that 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.
mesh_terms: D000105:Acetyl Coenzyme A / Q000378:metabolism; D000818:Animals; D002951:Citrates / Q000096:biosynthesis* / Q000378:metabolism; D019343:Citric Acid; D005260:Female; D008293:Malates / Q000378:metabolism; D008930:Mitochondria, Liver / Q000378:metabolism*; D011773:Pyruvates / Q000378:metabolism; D019289:Pyruvic Acid; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D002951:Citrates; D008293:Malates; D011773:Pyruvates; D019343:Citric Acid; C007744:fluorocitrate; D000105:Acetyl Coenzyme A; C030298:malic acid; D019289:Pyruvic Acid