MONOUNSATURATED FATTY ACIDS 69 



is a major metabolic fate of the unsaturated fatty acids. 

 In organisms such as C. butyricum and E. coli, which con- 

 tain both Ci6 and Cis unsaturated fatty acids, "methylation" 

 takes place with formation of a mixture of C17 and C19 

 cyclopropane fatty acids (see Chapter 2, section 5). 



The chemical nature of the cyclopropane fatty acids, 

 which arise when the microorganisms are cultured on oleic 

 rather than on c?5-vaccenic acid, remains to be established— 

 but two possibilities exist for oleic acid metabolism. Either 

 the double bond undergoes isomerization with formation 

 of czVvaccenic acid, which in turn is metabolized to lacto- 

 bacillic acid, or the bacteria have the ability to "methylate" 

 oleic acid with formation of one of the optical isomers of 

 dihydrosterculic acid. O'Leary (9) suggested that L. arahin- 

 osus brings about isomerization of added oleic acid with 

 formation of czVvaccenic plus lactobacillic acids, but his 

 experimental evidence in support of this unlikely course is 

 not convincing. We find (10) that oleic acid grown L. 

 delbrueckii produce a liquid saturated fatty acid fraction 

 which exhibits 1.6 times the growth promoting activity of 

 pure lactobacillic acid in L. delbrueckii assays. Since di- 

 hydrosterculic acid, which contains the methylene bridge 

 in the 9,10-position, is 1.4 times as active in the same assay 

 as lactobacillic acid with the 11,12-methylene bridge, we 

 concluded (10) "that oleic acid stimulates L. delbrueckii 

 to produce a 'saturated' fatty acid exhibiting higher micro- 

 biological activity than that of lactobacillic acid." 



Scheuerbrandt et al. (6) using C. butyricum demonstrated 

 that this organism does not interconvert unsaturated fatty 

 acids containing 5 methylene groups between the methyl 

 terminus and the double bond into fatty acids having 7 

 methylene groups in that location. Thus, the available 

 evidence suggests that the organisms are capable of bringing 



