MODES OF LINKAGE BY COVALENT BONDS 75 



isolation. Serine is the base which takes the place of choline, and the 

 phosphatidylserines have the following structure : 



O 



li 

 O CH-— O— C— R 



II I 



R— C— O— CH O 



I II 



CH2— O— P (O)— O— CH2— CH— COH 



OH NH2 



L — phosphatidylserine 



(d) Plasmalogejis or acetalphosphatides — In the pure state, the acetal- 

 phosphatides are soluble in alcohol, glacial acetic acid and chloroform, 

 sparingly soluble in benzene, and insoluble in acetone and ether. They are 

 derivatives in which an aldehyde group is condensed with two hydroxyls of 

 glycerol to form an acetal (a gem-d\Q\htr). The third glycerol hydroxy 1 is 

 esterified with an aminoethanol-phosphate residue. 



H 



H— C— O H -X X 



\| 

 C— R 



H— C— O' O H H _. 



HC— O— P — O— C— C— NHo 



I OH I I ' --^.IL^-' 



H H H 



2. Phosphoinositides 



These complex lipides containing inositol are numerous and little is 

 known about them. 



3. Sphingolipides 



In these complex lipides the alcohol is not glycerol but sphingosine, 

 a C18 aminoalcohol. 



CH3— (CH,)io— CH=CH— CH(OH)— CH(NHo)— CH2OH 



Sphingosine 



{a) Sphingomyelins or phosphosphingosides — The pure crystalline sphin- 

 gomyelins are insoluble in ether and acetone, but soluble in benzene, hot 

 ethanol and hot ethyl acetate. They are emulsifiable with water. 



