70 FATTY ACID METABOLISM IN MICROORGANISMS 



about "methylation" of double bonds in long-chain fatty 

 acids with double-bond locations five and seven methylene 

 groups removed from the methyl end with formation of 

 the corresponding cyclopropane fatty acids. However, iso- 

 lation and careful chemical characterization of the "methyla- 

 tion product" of oleic acid must be carried out in order to 

 establish this point unequivocally. 



Mention was made in Chapter 1, section 6, of the experi- 

 ments of Cheng et al. (11) who showed that a number of 

 position isomeric octadecanoic acids possessing both cis and 

 trans double bonds have the ability to stimulate growth of 

 L. arahinosiis on suboptimal amounts of biotin. The mode 

 of action of such acids is at present obscure. The possibility 

 exists that they may be converted into the corresponding 

 position isomeric cis or trans cyclopropane acids and that 

 these may have the ability to serve as metabolic substitutes 

 for lactobacillic acid. However, it seems unlikely that a 

 family of compounds of such widely differing structure and 

 belonging to different stereochemical series should be ca- 

 pable of performing the same or similar functions in micro- 

 bial metabolism. Similar arguments may be raised con- 

 cerning the mode of action of the polyunsaturated fatty 

 acids (linoleic, linolenic, and arachidonic), which are also 

 capable of promoting growth of lactic acid organisms on 

 biotin deficient media. Are these polyunsaturated acids un- 

 dergoing "methylation" with formation of acids containing 

 more than one cyclopropane ring? 



Studies on the metabolic fate of these various acids and 

 a better understanding of the role of the cyclopropane fatty 

 acids in microbial metabolism should aid in clarification of 

 these questions. 



