HYDROLYSIS PRODUCTS OF PHOSPHOLIPIDS 247 



This reaction can be brought about by transmethylation with methionine. 

 On the other hand, Stetten''- was of the opinion that no appreciable amount 

 of ethanolamine is converted to glycine, although the reverse reaction 

 readily occurs. However, White et al.,^^ in their recent textbook, have 

 pictured the conversion of ethanolamine to glycine by the pathway illus- 

 trated below. 



CH2CH2NH2 > CHoCHO > CH2COOH 



i 



H OH OH 



Ethanolamine Glycolaldehyde Glycolic acid 



> CH— COOH > CH2COOH 



II I 



O NH2 



Glyoxylic acid Glycine 



The Conversion of Ethanolamine to Glj'cine*' 



The relationship of these several nitrogenous bases to each other, as sug- 

 gested by Stetten, is illustrated in the accompanying schematic diagram. 



Betaine > Glycine > Ethanolamine > Choline 



Methyl Methyl 



Schematic Diagram to Illustrate the Synthesis of Choline from Betaine, Glycine, and 



Ethanolamine'^ 



When ethanolamine or choline is included in the diet, it is rapidly incor- 

 porated into the phospholipids;'^- it was fomid that these compounds re- 

 placed an equal amount in the tissue phospholipids. Insofar as choline is 

 concerned, the reaction proceeded most rapidly in the liver' and was slow- 

 est in the brain. 



(3) Serine 



Serine, HOCH2-CH(NH2) -COOH, has only recently been recognized as 

 a normal component of one type of phospholipids; thus, Folch and Schnei- 

 der''^ proved the presence of this amino acid combined in the phosphatide 

 molecule. This variety of compomid is now referred to as "phosphatidyl- 

 serine." 



As indicated in the preceding section, serine is readily converted to eth- 

 anolamine, as well as to glycine.''^ It has also long been recognized that the 



*' A. White, P. Handler, E. L. Smith, and De W. Stetten, Jr., Principles of Biochem- 

 istry, McGraw-Hill, New York, 1954, pp. 491, 554. 



