FATS AS ESSENTIAL DIETARY COMPONEXTS 



891 



as has also the trans-isomer of this compound.-^" Shiill el al.~^° found vac- 

 cenic acid about as effective as oleic acid in replacing biotin, both in the 

 basal medium and in the arginine-tyrosine medium. The trans forms of 

 these acids are usualh' equally potent, although marked variations do occur 

 in some cases. Cheng and her associates'^^ found that elaidic acid posses- 

 ses the highest potency of any of the octadecenoic acids tested. As the 

 double bond shifts in either direction from the 9 position, a reduction in 

 potenc}' occurs, until at the 6 position the acids are completely inactive. 

 Similar results are noted in the case of octadecenoic acid, which forms no 

 geometric isomers. These results are summarized in Table -i. 



Table 4 



BioTiN-LiKE Effect of Octadecenoic Acids and Linoleic Acid, 



Alone and with Biotin, Using LactobaciUus Arahinosus" 



" A. L. S. Cheng, S. M. 

 192, 611-622, 1951. 

 * No geometric isomers 



Greenberg, H. J. Deuel, Jr., and D. Melnick, /. Biol. Chem., 



of this compoimd. Included in cis column for convenience. 



c. Comparative Potency of Other Unsaturated Acids and of Related 

 Compounds. Axelrod and co-workers^^^ reported that a number of com- 

 pounds related to oleic acid are effective stimulants for the growth of 

 Lactobacillus arahinosus in the absence of biotin. The following activities 



-^ G. M. ShuU, R. W. Thoma, and W. H. Peterson, Arch. Biochem., 20, 227-241 

 (1949). 



