THE CEPHALINS 453 



the phosphate radicals are in meia position to each other. The structure 

 assigned is given herewith, R and R' referring to unkno\\ii groups. 



Diphosphoinositide is a white gritty powder, not emulsified in water and 

 insoluble in most organic solvents with the e.xception of wet chloroform. 

 It contains 7.3% phosphorus. Fatty acids, glycerol, and inositol metaphos- 

 phate are present in approximately equimolecular amounts. The inositol 

 meiaphosphate accounts for all the phosphorus in the molecule. Diphos- 

 phoinositide is an acidic phosphatide and, when prepared from brain tissue 

 with neutral solvents, it is obtained as the calcium and magnesium salt in 

 a base-to-phosphorus ratio indicative of a monophosphate. 



(5) Distribution of Phosphatidylethanolamine and Phosphatidylserine 



Although the methods for separation of the cephalin fractions employed 

 by Folch'--'' are not quantitative, the approximate quantities of the several 

 fractions in ox brain, correcting for 100% recovery and for the mixed frac- 

 tions, are as follows: phosphatidylethanolamine, 23%; phosphatidylserine, 

 48% ; and inositol phosphatide, 29%. 



Artom,^"^ making use of his new method for the estimation of ethanolam- 

 ine and serine,-^" has reported the proportion of phospholipids containing 

 these nitrogenous compounds in rat tissues and in human plasma. These 

 results are recorded in Table 9. 



Table 9 

 Distribution of Individual Phospholipids in Rat Tissues" 



" Adapted from C. Artom, /. Biol. Chem., 157, 595-599 (1945). 

 ' Ether-soluble fraction of lipid extract. 



According to Artom^''^ the values obtained compare well with those for 

 phosphatidylethanolamine found by Chargaff et al.^^ by the isotope dilu- 



sos C. Artom, J. Biol. Chem., 157, 595-599 (1945). 



«•» E. Chargaff, M. Ziff, and D. Rittenberg, /. Biol. Chem., lU, 343-352 (1942). 



