Studies on the Control of Fatty Acid Metabolism

Abstract

Abstract An unsaturated fatty acid auxotroph of Escherichia coli designated civ-2 fao-6, unable to carry out β oxidation of fatty acids has been isolated and characterized. The mutant is devoid of acyl-CoA dehydrogenase activity, and has low levels of enoyl-CoA hydrase and β-hydroxyacyl-CoA dehydrogenase while the activities of acyl-CoA synthetase and thiolase are normal. Long chain unsaturated fatty acids with chain length up to C20 can meet the auxotrophic requirements of the mutant without further chain shortening. Fatty acid analyses of the phospholipids of cells grown on different unsaturated fatty acids confirm that a regulatory mechanism is operative in E. coli that minimizes variations in the physical properties of phospholipids. When Δ11-eicosenoic acid was supplied, the phospholipids contained a low level of unsaturated acid but a high proportion of C14:0 was detected. Synthesis in vivo of fatty acids indicated that fatty acid synthetase is responsive to requirements for membrane lipid synthesis. This relationship is lost in the assay in vitro in which a high proportion of C18:0 is synthesized. Besides trans-octadecenoic acids, cis-Δ6-octadecenoic acid was found to cause cell death at low temperature. At 27°, death of elaidate-grown cells is associated with loss of crypticity to o-nitrophenyl-β-d-galactopyranoside hydrolysis, and is prevented by oleate which is incorporated into all major phospholipids.