CHAPTER V 



CHEMISTRY OF THE PHOSPHATIDES 

 AND CEREBROSIDES 



A. PHOSPHATIDES 



1. In I rod net ion ' 



The phosphatides represent a group of combined or conjugated lipids 

 which have the common property of containing a phosphate radical in 

 their molecules. In the case of the phosphatidic acids, phosphoric acid 

 is the only component in addition to the glycerol and fatty acids ordinarily 

 present in the neutral fats. However, the chief phosphatides or phos- 

 pholipids also contain one or two nitrogenous components. These may 

 be divided into the compounds in which the N :P ratio is 1 : 1 (mono-amino- 

 phosphatides), and a second group in which a 2:1 ratio exists between 

 nitrogen and phosphorus (di-aminophosphatides). In the case of lipositol, 

 a carbohydrate-like compound appears to be present in the molecule. 



It is interesting that the fats as well as the carbohydrates should have 

 phosphate derivatives of such great importance. In the case of the sugars, 

 phosphorylation seems in some way to be a prerequisite for enabling the 

 molecule to undergo the transformations which occur in ordinary metab- 

 olism. The same function may be assigned to phosphorylation in the 

 case of the lipids ; there seems to be little doubt that a larger proportion of a 

 phosphatide such as lecithin is always found in those organs in which active 

 metabolic changes in fat are presumably taking place, while the phospha- 

 tides are almost completely absent from the fat depots whose chief function 

 is the storage of this foodstuff. Moreover, the phosphorylated fats 

 (principally lecithin and cephalin) are present, also, in increased amounts 

 whenever fat is being transported to or from the fat depots of the body. 



However, in some cases phosphatides may not necessarily represent a 

 form of fat which is undergoing metabolic alteration or is in the process of 

 transport from one site to another. Such compounds may occur as a 

 portion of the structural element of an organ. It is generally believed 

 that the high concentration of sphingomyelin and even of lecithin in brain 

 and other nervous tissue is not related to its metabolic function under such 

 conditions. In fact, there is ample evidence that carbohydrate is the 

 principal source of energy for the nervous tissue. Possibly, the chemical 

 make-up of the phosphorylated fats renders them especially satisfactory 



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