184 III. OXIDATION AND METABOLISM 



Reiser^^" reported an increase in tetraenoic acids in the tissues of growing 

 chicks on a fat-free diet when cottonseed oil or ethyl linoleate was fed. 

 The increase was minimal in the neutral fat fraction of the carcass, more 

 pronounced in the organ neutral fat, and increasingly greater in the carcass 

 and organ phospholipids. In other studies,^^^'^^^ it was found that the 

 unsaturated acids reached their minimum value in egg yolks after the hens 

 had been fed a fat-free diet. Phospholipids were stored more efficiently 

 than was neutral fat.^^* It was noted that tetraenoic acids made their 

 appearance in the yolk after cottonseed oil or ethyl linoleate had been 

 fed.«23 



The most convincing proof for the synthesis of arachidonate from lino- 

 leate has been adduced by the use of tagged molecules. The mechanism 

 of the change of one unsaturated acid to another is largely a matter of 

 conjecture. Reiser ^^^ suggested that "fragments of the ingested acids 

 containing the double bonds might combine to form the more highly 

 unsaturated members of the series." Thomasson^^'* is in agreement with 

 Greenberg,^^^ who suggests that two molecules of linoleate give rise to one 

 of arachidonate. Sinclair^-^ is likewise convinced of the synthesis of 

 arachidonate from linoleate, "despite the improbability of a change involv- 

 ing the addition of two carbon atoms and desaturation at the 5:6 and 

 8:9 positions." Experimental evidence for these several conjectures 

 was adduced by Mead and co-workers^-'' who showed that, when carbox- 

 yl-labeled acetate was injected into intact weanling rats, it appeared as 

 the carboxyl carbon of arachidonic acid, as determined from the analysis 

 of the degraded octabromides prepared from the acids separated from 

 the tissues. 



On the basis of a survey of the literature, Holman'^-'^ concluded that 

 arachidonic acid does not occur in plants or in vegetable oils. He suggested 

 that the one positive report was probably based upon a typographical 

 error, and that arachidic acid was actually referred to. However, ara- 



«2o R. Reiser, J. Nutrition, 43, 325-336 (1950). 

 "1 R. Reiser, /. Nutrition, 40, 429-440 (1950). 

 «" R. Reiser, B. Gibson, M. J. Carr, and B. G. Lamp, /. Nutrition, 44, 159-175 (1951). 



623 R. Reiser, Arch. Biochetn. Biophys., 32, 113-120 (1951). 



624 H. J. Thomasson, Intern. Rev. Vitamin Research, 25, 62-82 (1953). 



62^8. M. Greenberg, Essential Fatty Acids, Dissertation, Dept. Biochem. Nutrition, 

 Univ. Southern California, 1951. 



626 H. M. Sinclair, Essential Fatty Acids and Their Relation to Pyridoxine, in R. T. 

 Williams, Lipid Metabolism, Biochem. Soc. Symposia No. 9, Cambridge Univ. Press, 

 80-99, 1952. 



627 J. F. Mead, G. Steinberg, and D. R. Howton, J. Biol. Chem., 205, 683-689 (1953). 



628 R. T. Holman, Personal communication, 1955. 



