The role of microsomes in fatty acid synthesis from acetate by cell-free preparations of rat liver and mammary gland

Abstract

1. 1. The conversion of acetate to fatty acids by particle-free supernatant and microsomal fractions of rat livers and of lactating and non-lactating rat-mammary glands was studied. 2. 2. Stimulation of fatty acid synthesis by addition of microsomes to the supernatant fraction was related to the amounts of microsomal protein and ATP added to the incubation mixtures. Excessive amount of either one depressed the level of synthesis, which could be reversed by addition of larger amounts of the other. 3. 3. Microsomal stimulation cannot be explained solely by the presence of microsomal ATPase since the highest level of synthesis was observed at a critical ratio of microsomal protein to ATP concentration. This suggests that microsomal stimulation is related to an ATP-dependent process. 4. 4. The newly synthesized fatty acids were firmly bound to the incubated protein. Upon re-isolation of microsomes at the end of incubation, it was found that 80% of the newly synthesized fatty acids was bound to these particles. However, microsomal stimulation cannot be explained solely on the basis of a binding phenomenon. 5. 5. The possibility that microsomal stimulation of fatty acid synthesis from acetate or acetyl-CoA is due to an effect on acetyl-CoA carboxylase present in the supernatant fraction is discussed.