460 V. CHEMISTRY OF PHOSPHATIDES AND CEREBROSIDES 



similar product has been found in such animal products as egg-yolk, ■''"•^■''^ 

 milk,^^" and fish sperm, ^^^ as well as in plant sources such as the ectoplasm 

 of the yeast cell.^" The principal fatty acid in the sphingomyelin of milk 

 lipids is lignoceric.^^^ 



The quantitative relationships of sphingomyelin in a number of human 

 tissues have been reported by Thannhauser et at.,^^^ who made use of a new 

 method for the determination of lecithin, cephalin, and sphingomyelin.^' 

 The following average values were found in per cent of dried tissue for 

 total phospholipid and sphingomyelin, respectively: brain, 30.90, 5.66; 

 lung, 6.65, 1.45; spleen, 8.56, 0.86; kidney, 8.00, 0.72; liver, 9.80, 0.38; 

 and heart, 6.87, 0.34. It is thus apparent that, with the exception of the 

 brain and lungs, in Avhich the sphingomyelin accounts for 20% of the total 

 phospholipid, in most organs sphingomyelin usually comprises only from 5 

 to 10% of the total phospholipid. 



Schmidt and collaborators'^^ have noted differences in the distribution 

 of sphingomyelin in man and in rats. In the rat brain, only about 5% of 

 the total lipid phosphorus was sphingomyelin phosphorus; on the other 

 hand, the sciatic nerve contained as high as 32% of this fraction. Sphingo- 

 myelin comprised the following percentages of total phospholipids in other 

 rat tissues: liver, 2.6; kidney, 14.0; lung, 14.0; spleen, 14.1; and heart, 

 4.9. In the cat, 24% of the total phospholipid was sphingomyelin and 

 50.0% of the sciatic nerve was composed of this compound. In beef brain, 

 the white matter was shown to have four times as much sphingomyelin as 

 the grey matter. 



6. The Phosphatidic Acids 



Chibnall and Channon^^'-^^^-'"-'^^ first isolated this type of phosphatide 

 from cabbage leaves and also from spinach. Such compounds have a typi- 

 cal phosphatide structure except that no nitrogenous base is present. In 

 plants, the phosphoric acid is usually combined with calcium. When cal- 

 cium is removed from this product, the corresponding diglyceride phos- 

 phoric acid or phosphatidic acid is formed. Such acids are thick oils which 

 darken on oxidation, under which condition they are no longer soluble in 

 ether. It is not known how extensively they are distributed in nature, as 



359 M. Stern and H. Thierfelder, Z. physiol. Chem., 53, 370-385 (1907). 



360 T. B. Osborne and A. J. Wakeman, /. Biol. Chem., 21, 539-550 (1915). 

 3" J. Schumacher, Cenlr. Bakt. Parasitenk., I, Orig., 108, 193-207 (1928). 



362 F. E. Kurtz and G. E. Holm, J. Dairy Sci., 22, 1011-1015 (1939). 



363 S. J. Thannhauser, J. Benotti, A. Walcott, and II. Reinstein, J . Biol. Chem., 129, 

 717-719 (1939). 



36^ G. Schmidt, J. Benotti, B. Hershman, and S. J. Thannhauser, J. BioL Chem., 166, 

 505-511 (1946). 



36* A. C. Chibnall and IT. J. Channon, Biochem. J., 21, 225-232 (1927). 

 »«« A. C. Chibnall and H. J. Channon, Biochem. J., 23, 176-184 (1929). 



