64 II. BIOSYNTHESIS 



amino acids, only methionine is lipotropic. On the other hand, such amino 

 acids as glycine, alanine, serine, tyrosine, proline, glutamic acid, and as- 

 paragine, did not augment phospholipid turnover as measured by the 

 incorporation of P'^ into these molecules. ^^^ Moreover, taurine, creatine, 

 di-(jQ-hydroxyethyl) sulfoxide, and sarcosine were entirely inactive in stimu- 

 lating phospholipid synthesis. *^^ 



Ethanolamine was found by Stetten-^" to stimulate phospholipid synthe- 

 sis in adult rats, although aminoethylphosphate was reported by Chargaff 

 and Keston^^- to be less effective than labeled inorganic phosphate in effect- 

 ing this synthesis. Artom and Cornatzer^^^ observed that choline stimu- 

 lated the synthesis of choline phospholipids only. However, ethanolamine, 

 methylethanolamine, and dimethylethylethanolamine, which also in- 

 creased phospholipid synthesis, produced this effect on both the choline- 

 containing and the non-choline-containing phospholipid fractions. Ac- 

 cording to a later report by these workers, ^^* other agents were found to 

 stimulate phospholipid synthesis; these included diethanolamine ((HOCH2 • - 

 CH2)2NH), triethanolamine ((HOCH2-CH2)3N), ethylethanolamine 



(HOCHz-CHaNHCaHs), diethylethanolamine (HOCH2-CH2N(C2H5)2), tri- 



+ 

 ethylcholine ((C2Hb)3NCH2-CH20H), and ethylamine (C2H5NH2). The 

 opinion is expressed that the stimulating action of lipid phosphorylation in 

 the liver requires a lower degree of structural specificity than do other 

 biological reactions mediated by the same substance. On the other hand, 

 Morton and Schwartz^^^ reported that the thyrotropic hormone of the 

 pituitary (TSH) causes an increase in thyroid lipids by 184%, as deter- 

 mined by in vitro studies, whereas there was no evidence of any increase in 

 P^- in the kidney or hver lipids. 



(4) The Biosynthesis of the Nitrogenous Bases of Phospholipids 



Although the component fatty acids of phospholipids, as well as the 

 glycerol and phosphoric acid, ordinarily pose no difficulty in the biosyn- 

 thesis of the several phospholipids, since they usually occur in the tissues 

 in adequate amounts, the absence or low concentration of the nitrogen- 

 containing component at the site of synthesis may under some conditions 

 be a limiting factor in this new formation of phosholipids. 



a. Ethanolamine. Ethanolamine, HOCH2-CH2NH2, which is a neces- 

 sary component of the phosphatidylethanolamine molecule, is also an 



322 E. Chargaff and A. S. Keston, /. Biol. Chem., 134, 515-522 (1940). 



323 C. Artom and W. E. Cornatzer, J. Biol. Chem., 176, 949-959 (1948). 



324 W. E. Cornatzer and C. Artom, J. Biol. Chem., 178, 775-787 (1949). 

 326 M. E. Morton and J. R. Schwartz, Science, 117, 103-104 (1953). 



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