Control of fatty-acid biosynthesis by long-chain acyl CoAs and by lipid membranes.

The possibility of a regulatory role of long-chain acyl-CoAs was studied in a system synthesizing palmitoyl-CoA and stearoyl-CoA in vitro. This system contained acetyl-CoA carboxylase (yeast), fatty acid synthetase (yeast) and lipid membranes as acceptors for the long-chain acyl-CoA compounds. In this system acetyl-CoA carboxylase is controlled by long-chain acyl-CoAs, whereas this is not true for fatty acid synthetase. The degree of inhibition of acetyl-CoA carboxylase depends strongly upon the capacity of the lipid membrane to incorporate long-chain acyl-CoAs. This capacity is not fixed but is a function of different parameters such as surface charge of the membrane. The effects of inositol deficiency in vivo (overproduction of lipids) and the shift to shorter chain lengths of the fatty acids synthesized under anaerobic conditions are discussed and interpreted.