[Control of lipogenesis in rat liver by changing the enzyme activity of the citrate-pyruvate system of acetyl coenzyme A transport].

The effects of insulin and tyroxin on the activities of pyruvate kinase, pyruvate dehydrogenase, ATP-citrate-lyase, NADP-malate dehydrogenase (decarboxylase), lactate dehydrogenase and on that of pyruvate carrier in rat liver were investigated. Insulin increased the activities of all the enzymes tested. The total activity of lactate dehydrogenase was not altered thereby; however, a redistribution of isoenzymes towards an increase in LDH1 and a decrease of LDH4 was observed. No increase of the pyruvate kinase, ATP-citrate-lyase and NADP-malate dehydrogenase activities took place, when actinomycin D was injected simultaneously with insulin. Tyroxin decreased the activities of pyruvate kinase, pyruvate dehydrogenase and ATP-citrate-lyase and increased that of NADP-malate dehydrogenase. The role of induction by insulin and inhibition by tyroxin of the enzyme activity in the citrate-pyruvate system of CoASA transport in lipogenesis control in rat liver is discussed. It is assumed that when lipogenesis is stimulated by insulin, the malate oxidized by the malate dehydrogenase reaction is formed in the cytoplasm, while under tyroxin action it is produced by the mitochondria.