PHOSPHOLIPIDS 65 



important precursor of choline. Stetten^^^ found that serine containing 

 N^^ was converted to ethanolamine by the rat. The conversion of the 

 amino acid to the base resulted from its decarboxylation on catalysis with 

 carboxylase, as shown below : 



H Carboxylase 



HOCHrC-COOH > HOCHz-CHaNHz + CO2 



I 

 NH2 



Serine Ethanolamine 



The Conversion of Serine to Ethanolamine 



After the administration of ethanolamine to rats, Stetten and GraiP" noted 

 an excessive accumulation of cephalin in the liver. 



Glycine is another amino acid reported by Stetten^^o to be extremely 

 active as a precursor of ethanolamine. Glycine may be transformed in- 

 directly to ethanolamine via serine. Winnick et al.^-^ found that liver 

 homogenate which had been incubated with glycine-C^^ contained serine 

 which must have originated from glycine. Sakami^-^ confirmed the role 

 of glycine in serine synthesis and showed that the third carbon required 

 for this reaction was a formate molecule likewise derived from another 

 glycine molecule.**" Siekevitz, Winnick, and Greenberg,**^ using a dif- 

 ferent isotope technic from that employed by Sakami, likewise confirmed 

 the fact that the formate required for the synthesis of serine from glycine 

 originates from a glycine molecule. Since serine is known to give rise to 

 ethanolamine, its intermediate formation in the conversion of glycine to 

 ethanolamine may be a normal one. 



Ethanolamine can form choline (see below), but choline cannot be 

 changed to ethanolamine.-*^ 



b. Choline. Ethanolamine was shown by Stetten, 2^" and by du Vigneaud 

 and associates, **2 to be the mother substance of choline. As pointed out 

 earlier, ethanolamine can arise from serine, which in turn is synthesized 

 from glycine. Ethanolamine can be methylated by methionine. **2 Steen- 

 sholt*** made the interesting observation that, in the methylation of 



326 De W. Stetten, Jr., /. Biol. Chem., I44, 501-506 (1942). 



3"De W. Stetten, Jr., and G. F. Grail, /. Biol. Chem., I44, 175-181 (1942). 



32« T. Winnick, I. Moring-Claesson, and D. M. Greenberg, /. Biol. Chem., 175, 127-132 

 (1948). 



"9 W. Sakami, /. Biol. Chem., 176, 995-996 (1948). 



3M W. Sakami, Federation Proc, 8, 246 (1949). 



"1 P. Siekevitz, T. Winnick, and D. M. Greenberg, Federation Proc, 8, 250 (1949). 



332 V. du Vigneaud, J. P. Chandler, M. Cohn, and G. B. Brown, /. Biol. Chem., 134, 

 787-788 (1940); V. du Vigneaud, M. Cohn, J. P. Chandler, J. R. Schenck, and S. Sim- ^ 

 monds. Ibid., I40, 625-641 (1941). •• ', p ?"7\ 



3" G. Steensholt, Acta Physiol. Scand., 17, 276-279 (1949). ' \^l • \ 



'.. \ I) » i?, ;^ -- 1 p-? ) 



