BIOSYNTHESIS OF CYCLOPROPANE FATTY ACIDS 49 



H H 



;< 



H3C— (CH2)5 — ^ ^» — (CH2)9— COOH 



(I) 



H3C— (CH2)5 — C ■ C — (CH2)9— COOH 



H H 



Fig. 2.6, Biosynthetic route to lactobacillic acid. 



lactobacillic acid molecule. The experimental evidence 

 for this rather novel biochemical reaction stems from studies 

 on the distribution of radioactivity in individual fatty acids 

 isolated from L. arabinosus grown on such various radio- 

 active precursors as aVvaccenic acid-l-C^^, methionine 

 methyl-C^^, and formate-C^^, respectively (21, 22). In ex- 

 periments in which the bacteria grow on media low^ in 

 biotin in presence of carboxyl labeled cf^-vaccenic acid 

 (6.72 X 106 c.p.m.), 1.26 X 10^ c.p.m. or 18.7% of the radio- 

 activity is associated with the cells. The distribution of 

 label among the various fractions (Table 2.5) shows that 

 99.2% of this radioactivity is located in the fatty acid frac- 

 tion; the other cellular constituents are practically inactive. 

 The major proportion of activity is located in the unsatu- 

 rated ("dihydroxy") fatty acid and lactobacillic acid frac- 

 tions; capric, lauric, myristic, and palmitic acids and the 

 nonsaponifiable material show negligible labeling (Table 

 2.6). The specific activity of the "dihydroxy" (1.10 X 10^ 



