The biosynthesis of cyclopropane fatty acids. I. Feeding experiments with oleic acid-9,10-d₂, oleic acid-8,8,11,11-d₄, and L-methionine-methyl-d₃

cis-9-Octadecenoic acid-9,10-d 2 and cis-9-octadecenoic acid-8,8,11,11-d 4 and L-methionine-methyl-d 3 were administered to cultures of Lactobacillus plantarum and converted by the organism to the corresponding cyclopropyl compounds. The first experiment showed that no scrambling or loss of label occurred when a methylene unit was added across the double bond of the labelled substrate. In the second experiment, again, no loss or scrambling of label occurred, a result which ruled out any mechanism for biological cyclopropanation involving allylic activation of the double bond. The third experiment yielded a biosynthetic cyclopropane fatty acid containing deuterium located exclusively at the methylene group of the cyclopropane ring. Up to 17% of a d 1 -species accompanied the major dideuterated compound. The lone deuterium in the d 1 -cyclopropane fatty acid occupies both positions of the methylene group to the same extent. It has been shown that the extent to which d 1 -cyclopropane fatty acid is produced increases with cell growth. The extent of exchange was similar in the cyclopropanation of both the 9,10-and 11,12-isomers of cis-octadecenoic acid.