Studies on the biosynthesis of cyclopropane fatty acids in Escherichia coli

By use of various mutants either defective in unsaturated fatty acid biosynthesis or altered in the level of S-adenosylmethionine we have tested the effects of changes in the intracellular concentrations of these substrates on in vivo cyclopropane fatty acid synthesis. A 1.5-fold change in unsaturated fatty acid content produced an equivalent change in cyclopropane fatty acid content. A 20-fold difference in S-adenosylmethionine content had little or no effect on cyclopropane fatty acid formation. Studies with unsaturated fatty acid auxotrophs showed that unsaturated fatty acid synthesis is not required for cyclopropane fatty acid synthesis. Other studies demonstrated that cyclopropane fatty acid content had little effect on phospholipid stability. Finally, we have shown by three methods (gas-liquid chromatography, proton and ¹⁵C nuclear magnetic resonance spectra) that the cyclopropane ring of these Escherichia coli acids has the cis configuration.