54 FATTY ACID METABOLISM IN MICROORGANISMS 



thionine-methyl-C^* into the lactobacillic acid molecule, 

 but he did not elucidate the exact position of the label. 

 In their use of gas chromatography for separation of fatty 

 acids, Innes Chalk and Kodicek (25) observed incorporation 

 of methionine-methyl-C^* into lactobacillic acid with E. coli 

 and L. casei. In L. casei all the label was located in the 

 lactobacillic acid, which is the sole cyclopropane fatty acid 

 present. In E. coli which contains both lactobacillic acid 

 and its lower homolog c/5-9,10-methylenehexadecanoic acid, 

 the label was distributed between these acids in the pro- 

 portion 42 to 58%. Incorporation of methionine-methyl 

 into cf5-9,10-methyleneoctadecanoic acid had been demon- 

 strated earlier (24). Although the exact position of the 

 label in the lower homolog of lactobacillic acid has not 

 been established by degradation, it appears very likely that 

 it is located in the methylene bridge carbon. Addition of 

 unlabeled formate to the growth medium of L. casei does 

 not affect incorporation of methionine-methyl-C^^ into the 

 lactobacillic acid molecule. Thus, the methyl group of 

 methionine is probably not incorporated into lactobacillic 

 acid via oxidation to "active formate" (25). 



The biosynthesis of 10-methylstearic acid from oleic acid, 

 which represents a major metabolic reaction of the latter 

 acid in Mycobacterium phlei (14), appears to be related 

 intimately to lactobacillic acid formation. However, there 

 is no net change in the oxidation state in lactobacillic acid 

 biosynthesis— in contrast to 10-methylstearic acid formation, 

 which must involve a reductive step. The methyl group of 

 methionine serves as the source for the extra carbon in 

 both processes. 



Addition of one-carbon fragments to double bonds pro- 

 vides a general biochemical mechanism for formation of 

 branched-chain compounds not only in the long-chain fatty 



