452 V. CHEMISTRY OF PHOSPHATIDES AND CEREBROSIDES 



that a similarity in structure obtains between brain inositol phosphatide 

 and soybean lipositol. The rate of hydrolysis of the two products is iden- 

 tical; the carbohydrate from both phosphatides is galactose. Finally, 

 tartaric acid is liberated, in either case, only if an alkaline hydrolysis is em- 

 ployed. 



Lipositol is a fine, creamy, white powder which is quite friable when dry. 

 On exposure to air, it darkens slowly. When no precautions are observed to 

 prevent oxidation during its preparation, one obtains a light brown rather 

 than a white powder. Lipositol dissolves in petroleum ether, benzene, di- 

 ethyl ether, and chloroform when they are moist, but it is insoluble in the 

 anhydrous solvents. Moreover, it is insoluble in ethanol, methanol, ace- 

 tone, and dioxane; it does, however, form an emulsion with water. 



a. Brain Diphosphoinositide. Considerable doubt is cast on the valid- 

 ity of the findings as to the purity of the original brain inositol phos- 

 phatides by the recent reports by Folch^"^-^"^ of the preparation of a rela- 

 tively pure brain diphosphoinositide w^hich contains small amounts of car- 

 bohydrate and only traces of carboxyl nitrogen. This product has been 

 separated from brain cephalin by fractionation with methyl alcohoP"''; 

 the separation is based upon the fact that brain diphosphoinositide is less 

 soluble in this solvent than are phosphatidylethanolamine or phosphatidyl- 

 serine. This sample contained 16% of inositol, which is the figure also ob- 

 tained for soybean lipositol. This fraction accounts for all the inositol in 

 the brain cephalin. The proportions of inositol, phosphoric acid, glycerol, 

 and fatty acid w^ere 1:2:1:1. It is not certain as yet whether a nitrogen- 

 containing compound is present as a portion of the molecule or whether it is 

 a contaminant. Folch^"*^ was able to separate inositol metadiphosphate 

 from the purified diphosphoinositide, following a short-time acid hydrolysis. 

 This compound has been identified on the basis of its elementary composi- 

 tion, by titration with alkali, by the isolation of inositol from it, and by a 

 study of its reaction products with HIO4. The last reaction proves that 



/OH 

 H 0-P=0 



HCOH HCOH 



I I /°" 



HCOH HC-OP=0 



V •■■ 



H OH 



Inositol metaphosphate 



.J. Folch, Federation Proc, 5, i:34 (1946). 



J. Folch, J. Biol. Chem., 177, 505-519 (1949). 



J. Folch, J. Biol. Chem., 177, 497-504 (1949). 



