312 ESSENTIAL FATTY ACIDS 



acid of beef tallow has been identified as m,as-9,12-linoleic acid, and the 

 linolenic acid from the same source as ds,as,CTS-9,12,15-linolenic acid, 

 which implies that these should function as essential fatty acids. ^ Canadian 

 lard^ has been found to contain, on the average, 8.7% of linoleic, 0.6% of 

 linolenic, and 0.4 % of arachidonic acid. Arachidonic acid has been identi- 

 fied^- ^ in pig back fat. The liquid fatty acids of shark liver oil,^ which are 

 60 % of the total, contain 15 % linoleic and 2.6 % linolenic acid. It is realized^ 

 that the fatty acid composition of oils such as linseed oil cannot be predicted 

 from the iodine value alone. Cardiolipin has been recognized^ as a complex 

 phosphatidic acid containing a large amount of linoleic acid. 



Relative reactivities toward hydrogenation have been noted^ for several 

 mono-, di- and triethenoic acids, and a saturase has been found ^ in pumpkin 

 seedlings. Oxidation of the essential fatty acids has been intensively studied, 

 both with soybean lipoxidase,!^-^^ which is specific for the essential fatty 

 acids, and with heme compounds.i^-^^ Both hemin and hemoglobin are de- 

 stroyed during catalyzed autoxidation of linoleic and linolenic acids, with 

 liberation of inorganic iron, under physiologic conditions. ^^ Crude linoleic 

 acid in the diet causes a progressive secondary anemia in rats." Oxygenated 

 linoleic acid is very susceptible to further oxidation. ^^ Copper, in trace 

 amounts, greatly accelerates autoxidation of linoleic acid,i^ and it has been 

 suggested that peroxides formed in the brain may be destroyed by linolenic 

 and linoleic acids in a reaction catalyzed by copper,^'' since the catalase con- 



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