50 II. BIOSYNTHESIS 



does not occur, since no good evidence for a trans -^ cis isomerization of the 

 fatty acids has been demonstrated in vivo. 



Miller and Burr-^" investigated the synthesis of phospholipids by the use 

 of fats containing fatty acids having characteristic absorption spectra. 

 These experiments were performed with tung oil, which is made up largely 

 of elaeostearic acid; the latter acid contains three conjugated double 

 bonds. 2*^ Acids having conjugated bonds can readily be detected because 

 of their characteristic absorption spectra. Fatty acids such as linoleic 

 acid, which do not have conjugated double bonds, have a low ultraviolet 

 absorption. However, Miller et alr^^ demonstrated that linoleate can be 

 converted to a conjugated acid having approximately 100 times the ab- 

 sorption coefficient of the original non-conjugated dienoic acid.^^^ It was 

 shown by Barnes and co-workers^*^ that conjugated fatty acids were in- 

 corporated into both the neutral fat and the phospholipid fraction of the 

 intestinal mucosa, although in this case the synthesis of neutral fat pro- 

 ceeded more rapidly than did that of phospholipid. 



Since the .development of the knowledge of isotopes, the incorporation 

 of labeled fatty acids into the phospholipid molecule has been used by a 

 number of workers as a method of studying the origin of these compounds. 

 Cavanagh and Raper^** employed a partially deuterated linseed oil and 

 followed the incorporation of the labeled fatty acids into the phospholipid 

 of the liver, brain, kidney, blood plasma, and blood corpuscles of rats. 

 Barrett, Best, and Ridout,^^^ and Sperry et al."^^^ likewise employed this 

 procedure to demonstrate the synthesis of phospholipids and fatty acids. 

 Among the workers who have followed the formation of phospholipids by 

 using fatty acids containing C^*, Stevens and Chaikoff^^ may be cited. 

 Although Levy-^^ was unable to demonstrate the presence of Cn, Cn, or 

 Ci4 acids in the phospholipids after feeding the triglycerides containing these 

 acids, Stevens and Chaikoff-^ reported that lauric (C12) and myristic (C14) 

 acids containing C^Mabeled carboxyl groups were incorporated into the 

 phospholipids. 



In addition to introducing the label into the fatty acid, tagging of other 

 components of the phospholipid molecule has been carried out. Inorganic 



230 E. S. Miller and G. O. Burr, Proc. Soc. Expil. Biol. Med., 36, 726-729 (1937). 

 2" E. S. Miller, R. H. Barnes, J. P. Kass, and G. O. Burr, Proc. Soc. Expti. Biol. Med., 

 41, 485-489 (1939). 



"2 R. H. Barnes, E. S. Miller, and G. O. Burr, Am. J. Physiol., 126, 427 (1939). 



233 R. H. Barnes, E. S. Miller, and G. O. Burr, /. Biol. Chem., I40, 233-240 (1941). 



234 B. Cavanagh and H. S. Raper, Biochem. J., 33, 17-21 (1939). 



235 W. M. Sperry, H. Waelsch, and V. A. Stoyanoff, /. Biol. Chem., 135, 281-290 (1940). 



236 M. Levy, Arch. sci. physiol, 4, 337-343 (1950). 



