800 XIII. ESSENTIAL FATTY ACIDS 



that liiioleif acid can be converted to arachidonic acid in the animal body,^^ 

 and that some synthesis and interconversion of fatty acids occur in the 

 body.^^™'^"* The transformation of linoleic acid involves the extension 

 of the carbon chain by two carbons, and a double desaturation at the car- 

 boxyl side of the original double bonds. Mead and co-workers^"^ proved 

 that isotopic acetate can be demonstrated in the arachidonic acid mole- 

 cules synthesized from linoleate. 



Barki et al.^^^ observed that mature rats could be maintained on a fat- 

 free diet for a prolonged period, without presenting deficiency symptoms, 

 except for emaciation. Moreover, when the depleted animals were fed the 

 fat-free diet ad libitum for a sufficient period, the EFA deficiency symptoms 

 disappeared spontaneousl3^ This suggests that some synthesis of the EFA 

 may occur. 



Greenberg^"^ suggested that one mole of arachidonic acid can arise from 

 two molecules of hnoleic acid. This viewpoint is supported by the findings 

 of Widmer and Holman,^"^ Reiser, ^"^'"^ and Holman,^^ who demonstrated 

 that, when dienoic and trienoic acids were fed, tetraenoic, pentaenoic, 

 and hexaenoic acids, respectively, were present in the organs and body fat 

 of rats,^^'^°^ in egg yolk,"" and in the body fat of chicks.'"" 



{6) The Biologic Activity of Related Compounds 



In addition to the three main EFA, linoleyl alcohol,'^ docosahexaenoic 

 acid, and two hexahydroxy stearic acids (linusic and isolinusic)'^ have been 

 reported to exhibit low degrees of activity in protecting against fat-defi- 

 ciency symptoms. However, Thomasson'^ observed that linusic acid pos- 

 sessed no bioactivity, and that the potency of isolinusic acid was only 

 slight. In addition, Thomasson^® recorded a biopotency of 43% for 1 1,14- 

 eicosadienoic acid and one of 9% for 10,13-nonadecadienoic acid. Accord- 

 ing to this author, the presence of double bonds on the 6 : 7 and 9 : 10 posi- 

 tions (counting from the terminal CHs group, or co-carbon) is required for 

 EFA activity. An increase in the number of double bonds on the CHg- 



93 L. C. A. Nunn and I. Smedley-MacLean, Biochem. J., 32, 2178-2184 (1938). 



10" I. G. Rieckehoff, R. T. Holman, and G. O. Burr, Arch. Biochem.., 20, 331-340 

 (1949). 



101 R. Reiser, J. Nutrition, 42, 325-336 (1950). 



i«2 J. F. Mead, G. Steinberg, and D. R. Howton, Federation Proc, 12, 244 (1953). 



103 V. H. Barki, H. Nath, E. B. Hart, and C. A. Elvehjem, Proc. Soc. Exptl. Biol. Med., 

 66,474-478(1947). 



10^ S. M. Greenberg, A Nutritional Evahiation of the Essential Fatty Acids in the Rat. 

 Dissertation, Univ. Southern Calif., Dept. Biochem. Nutrition, 1951. 



106 C. Widmer, Jr., and R. T. Holman, Arch. Biochem., 25, 1-12 (1950). 



i«6R. Reiser, /. Nutrition, 44, 159-175 (1951). 



