786 XIII. ESSENTIAL FATTY ACIDS 



to possess 100% biopotency as compared with linoleate. The conjugated 

 trienoic acid, a-elaeostearic acid (9,11,13-octadecatrienoic acid), was 

 reported by Burr, Burr, and Miller^^ to be ineffective in counteracting the 

 fat-deficiency synch'ome; confirmatory negative results have been re- 

 corded by Deuel et al.^^-'^'^ Tange -^ likewise noted that 4,8,12,15,19-docosa- 

 pentaenoic acid gave a negative biologic response. 



Thomasson'^ is of the opinion that the presence of double bonds at the 

 6:7 and the 9:10 positions (counting from the terminal CH^— group 

 (or co-carbon)) is essential for the biologic activity of the unsaturated 

 fatty acids. When the number of double bonds is extended on the CH3 — 

 side of these afore-mentioned positions, the bioactivity decreases, whereas 

 dehydrogenation on the carboxyl side does not weaken the EFA activity, 

 but may actually augment it. 



(S) Methods of Preparation of Polyunsaturated Acids 



a. Introduction. The preparation of pure polyunsaturated fatty acids 

 still poses a very difficult problem. This is especially the situation in the 

 case of arachidonic acid; variations in biologic response to this acid have 

 been attributed to differences in the purity of the samples assayed. 



If the source of the polyunsaturated acid is a tissue rather than a pure 

 fat or oil, the total lipid must first be extracted by some method of wet 

 extraction. For example, Holman and Greenberg^^ employ ethanol, 

 or ethanol-ether, as a solvent, or separate the acid after digestion of the 

 tissue with 30% potassium hydroxide. It is important to protect the 

 sample as much as possible during all stages of preparation, and for this 

 reason the reactions are generally carried out as far as is practicable under 

 nitrogen. After isolation of the lipid mixture, the material is saponified 

 (if this step has not been previously carried out), and the acid is freed, 

 washed, and dried. 



The saturated fatty acids may be removed from the mixture by the 

 lead soap ether or the lead soap alcohol method; these methods depend 

 upon the relative insolubility of the lead soaps of the saturated acids in 

 organic solvents. 



b. Low-Temperature Crystallization. The lead soap method for the 

 separation of the saturated acids has been largely replaced by several newer 



" G. O. Burr, M. M. Bvirr, and E. S. Miller, J. Biol. Chem., 97, 1-9 a932). 

 "^■^ H. J. Deuel, Jr., R. B. Alfin-Slater, A. F. Wells, G. D. Kryder, and L. Aftergood, /. 

 Nutrition, 55, 337-346 (1955). 



23 U. Tange, Sci. Papers Inst. Phys. Chem. Research (Tokyo), 20, 13-28 1932). 



" R. T. Holman and S. E. Greenberg, J. Am. Oil Chemists' Soc, SO, 600-601 (1953). 



