PHOSPHOLIPIDS 49 



phorus is given in the inorganic form.-^^"-^^ The tissues of these animals 

 were later shown to contain the normal amounts of phospholipids. More- 

 over, it has long been known that the phospholipids of the chick embryo 

 increase during the incubation of the egg; thus, Hevesy et al.--^ demon- 

 strated that the phosphohpids m the chick embryo are not derived from 

 the yolk, but are synthesized by the embryo itself. The subject of the 

 synthesis and orighi of phospholipids has been reviewed by Sinclair,^^^'^^^ 

 by Bloor,223 and by Chaikoff.^^^ 



{1 ) Methods for the Demonstration of Phospholipid Biosynthesis in vivo 



In addition to the balance experiments as proof of phospholipid syn- 

 thesis, direct evidence has been adduced by the use of a number of newer 

 procedures. London^-^ employed a unique method developed by himself, 

 by which it is possible to obtain blood from internal blood vessels of normal, 

 intact animals. He showed that the phospholipid content in the blood 

 leaving the liver was greater than that in the blood entering this organ. 



The use of unnatural fatty acids has afforded another method for the 

 study of the synthesis of phospholipids. One of these procedures involves 

 the use of elaidic acid, the trans-isomer of oleic acid, which is a foreign fatty 

 acid.--^ However, it behaves in vivo exactly as if it were a naturally occur- 

 ring fatty acid. Elaidic acid can be metabolized when fed in large amounts; 

 it is stored mainly in the fat depots by the rat.^"-^^* After being deposited 

 in the adipose tissues, it disappears slowly. ^^^ KohP"---^ reported that 

 the rate of disappearance of elaidic acid is 72 mg./hr. in rats fed elaidin 

 alone, and 35 mg./hr. in animals which received the elaidin along -wdth pro- 

 tein and sugar. It is not knowTi whether or not the elaidic acid is trans- 

 formed in the body by the process of desaturation, or by hydrogenation, 

 or to oleic acid by isomerization. However, the last procedure probably 



2" J. P. Gregersen, Z. physiol. Chem., 71, 49-99 (1911). 



*i8 E. V. McCollum, J. G. Halpin, and A. H. Drescher, /. Biol. Chem., 13, 219-224 

 (1912). 



215 R. H. A. PUmmer, Biochem. J., 7, 43-80 (1913). 



220 G. C. Hevesv, H. B. Levi, and O. H. Rebbe, Biochem. J., 32, 2147-2155 (1938). 



"1 R. G. Sinclair, Physiol. Revs., 14, 351-403 (1934). 



"2 R. G. Sinclair, Biol. Symposia, 5, 82-98 (1941). 



223 W. R. Bloor, Physiol. Revs., 19, 557-577 (1939). 



224 1. L. Chaikoff, Physiol. Revs., 22, 291-317 (1942). 



225 E. S. London, Ergeh. Physiol., 26, 320-369 (1928). 



226 R. G. Sinclair, /. Biol. Chem., Ill, 515-526 (1935). 



227 U. F. F. Kohl, /. Biol. Chem., 126, 709-719 (1938). 



228 M. F. F. Kohl, /. Biol. Chem., 126, 721-729 (1938). 

 "9 M. F. F. Kohl, J. Biol. Chem., 126, 731-736 (1938). 



