100 



LIPIDES (fats and RELATED SUBSTANCES) 



Phosphatidyl serine is a strong acid, existing at physiological pH values 

 combined as a salt with sodium or potassium. It is alcohol-insoluble, 

 whereas phosphatidyl ethanolamine is easily soluble in alcohol. The 

 ''cephalin" of beef brain, and of pig heart and liver, is made up mostly 

 of phosphatidyl ethanolamine (50-75 per cent), mixed with smaller 

 amounts of phosphatidyl serine (13-35 per cent) . According to Chargaff, 

 egg yolk cephalin is entirely of the ethanolamine type. Cephalins are 

 thought to play a part in the process of blood clotting. 



Sphingomyelins 



This type of phospholipide differs from most others in being insoluble 

 in ether. It is also insoluble in acetone, but forms a colloidal solution 

 in water. It can be extracted from tissues with hot alcohol, but on 

 cooling crystallizes out as a white solid. First discovered in brain tissue, 

 it is now known to occur in many organs, as well as in blood and milk. 

 Enormously increased amounts are present in all the organs and tissues 

 (except brain) of patients suffering from Niemann-Pick's disease. 



Sphingomyelin on hydrolysis gives rise to an amino alcohol (sphingo- 

 sine) , plus a fatty acid (usually lignoceric) , phosphoric acid, and choline. 

 The fatty acid is attached to the amino group to form the amide, ligno- 



CH3(CH2),2CH=CH-CH-CH— CH2 



I I I 



OH NH2 OH 



Sphingosine 



ceryl sphingosine. This substance is a normal component of pig spleen 

 and liver and can also be obtained by partial hydrolysis of sphingomyelin. 



CH3(CHo)nCH=CH-CH-CH— CH2 



I I I 



OH NH OH 



I 



CO 

 I 



(CH2)22 

 CH3 



Lignoceryl sphingosine 



The phosphoric acid and choline are presumably present in sphingomyelin 

 as a phosphorylcholine, inner-salt group (see formula of lecithin, p. 97) , 

 attached to one of the hydroxyl groups of sphingosine. 



Other phospholipides 



Almost nothing is known of the biological significance of the phospho- 

 lipides other than lecithins and cephalins, but the fact that they occur 



