On the Relationship between Fatty Acid Synthesis and the Total Activities of Acetyl Coenzyme A Carboxylase and Fatty Acid Synthetase in the Liver of Prenatal and Early Postnatal Chicks

Abstract

Abstract Fructose and lactate markedly stimulated fatty acid synthesis from [1-14C]acetate in isolated cells prepared from the livers of unfed neonatal chicks (21 or 22 days of incubation). In liver cells obtained from unhatched chicks (19 days of incubation) fructose and lactate had very small stimulatory effects on fatty acid synthesis. The increase in fructose- and lactate-stimulated fatty acid synthesis during hatching was about 20-fold. Pulmonary respiration began on the 20th day and the chicks were hatched by the 21st day. Fatty acid synthesis from [1-14C]acetate (plus citrate) or [1,5-14C]-citrate in a cytosol fraction of liver increased about 20-fold during the hatching period. Concomitantly, there were 6.5- and 4-fold increases in the total activities of acetyl-CoA carboxylase and fatty acid synthetase, respectively. The effect of hatching on the total activity of fatty acid synthetase could be mimicked by incubating 18-day-old embryos in an atmosphere of 100% oxygen for 24 hours. The oxygen treatment did not affect the total activity of acetyl-CoA carboxylase or the rate of fatty acid synthesis in isolated hepatocytes (plus or minus fructose). Injecting glucose or fructose into 18-day-old embryos had no effect on the total activity of acetyl-CoA carboxylase or fatty acid synthetase. Feeding the neonatal chicks increased the total activities of both acetyl-CoA carboxylase and fatty acid synthetase. If the neonatal chicks were not fed, the total activity of acetyl-CoA carboxylase did not change for at least 3 days. In contrast, the total activity of fatty acid synthetase continued to increase during those 3 days of fasting. The total activities of both enzymes were increased when unfed neonatal chicks were given a single glucose or fructose injection. The effect was not observed until 6 hours after administration of the sugar despite the fact that the rate of fatty acid synthesis was stimulated by more than 5-fold at 1½ hours after the injection. The results suggest that acetyl-CoA carboxylase and fatty acid synthetase are not part of an operon or its eukaryote equivalent, and that changes in their total activities did not initiate changes in the rate of fatty acid synthesis.