Fatty acid metabolism of isolated mammalian cells.

It is now clear that a wide variety of differentiated cells in culture exhibit essentially the full spectrum of mammalian fatty acid metabolism. These cells readily incorporate free fatty acids into membrane phosphoglycerides, modify exogenous fatty acids by desaturation and elongation, and store excess fatty acyl groups, primarily as triacylglycerols. Similarly, many different types of cells synthesize cyclooxygenase and lipoxygenase derivatives of long chain polyunsaturated fatty acids. Furthermore, although the fatty acid composition of cellular phospholipids can be modified by medium supplementation, cells in culture exhibit definite fatty acyl specificities for the various steps of fatty acid activation, transesterification and release. As the extensive repertoire of fatty acid metabolism in mammalian cells has been elucidated, and as the ability to grow differentiated cells in culture has increased, new questions have arisen. There is still much to be learned about the enzymes involved in synthesizing and maintaining the unique fatty acid composition of the different cellular phospholipids and the processes which regulate the desaturation, elongation and retroconversion of polyunsaturated fatty acids. Other areas of great current interest are the mechanisms by which certain long chain polyunsaturated fatty acids are made available for conversion to oxygenated, biologically-active derivatives, the metabolic interactions between different polyunsaturated fatty acids, particularly n-3 and n-6 fatty acids, the cellular roles of the C22 polyunsaturated fatty acids, and the functions of particular molecular species of phospholipids in membrane-mediated events. Further research in these areas will contribute to unravelling the role of fatty acids and fatty acid derivatives in the physiological processes of mammalian cells.