Citrate and the conversion of carbohydrate into fat. The regulation of fatty acid synthesis by rat liver extracts.

1. The rate of fatty acid synthesis by particle-free extracts prepared from rat liver is increased greatly if the enzyme system is first activated with citrate. 2. The extent of the activation depends on the citrate concentration and on the time of activation in an interdependent manner. 3. Citrate activation is strongly dependent on temperature. 4. Tricarballylate can replace citrate as an activator, but its presence in the assay inhibits fatty acid synthesis. 5. Mg(2+) ions can replace citrate in the activation but not in the complete reaction system. 6. ATP prevents the activating effect of citrate and Mg(2+) ions. 7. The rate of fatty acid synthesis is increased by palmitoyl-dl-carnitine. This type of activation, additional to that caused by citrate, is rapid and does not depend on prior incubation. 8. Inhibition of fatty acid synthesis by palmitoyl-CoA can be prevented by palmitoyl-dl-carnitine or by increasing the concentration of protein.