HYDROLYSIS PRODUCTS OF PHOSPHOLIPIDS 245 



line suggested by Siekevitz and Green])erg^^ involves the transfer of methyl 

 C to the |(3-carbon of serine. 



Mills^'^ reported an increased choline requirement in the case of rats kept 

 in a high environmental temperature. Johnson et al.^^ reported that only 

 approximately 1% of the choline intake was excreted as choline by man. 

 It was found to be present in undiluted sweat to the extent of 2.7 to 15.3 

 fjLg. %. However, the latter workers found no increase in choline excretion 

 by four adult male subjects kept under "hot moist" conditions. It is 

 therefore uncertain whether or not the choline requirement in the human 

 subject is augmented at high environmental temperatures. 



Busset®^ reported that, four hours after the administration of labeled 

 choline to a dog, it had passed through the wall of the small intestine, the 

 blood and the bile, where it was present in the amount of 7.2%. However, 

 there was no e^'idence of oxidation of this substance. Byerrum and Wing'" 

 reported that the methyl carbons of choline can be transferred to yield the 

 methyl groups in nicotine in the North American wild tobacco plant {Nico- 

 tiana rustica). The methyl carbons of choline and of methionine appeared 

 to be donated to this plant at about the same rate. Since there were no 

 detectable am omits of phospholipids, it was not believed that choline is 

 normally involved in the synthesis of these substances. 



d. Choline as a Source of Glycine. Choline is considered to be a precur- 

 sor of glycine in the intact rat. Soloway and Stetten'^^ noted that, when 

 N^Mabeled choline was injected into rats together with sodium benzoate, 

 a considerable amoimt of the excreted hippuric acid contained the glycine 

 fragment labeled with N^\ Betaine was equally active as a precursor, but 

 dimethylethanolamine was found to be far less efficient in this respect. It 

 was demonstrated by the use of doubly-labeled choline that the ethanolic 

 residue of choline, together with the attached nitrogen, is transformed in- 

 tact into glycine. It was postulated that an obligatory oxidation of cho- 

 line occurs, to yield betaine, prior to its demethylation to glycine.''^ 



{2) Eihanolamine 



a. Introduction. Ethanolamine, HOCH2-CH2-NH2, is of considerable 

 importance, inasmuch as it constitutes the nitrogenous constituent of the 



«8 P. Siekevitz and D. M. Greenberg, /. Biol. Chem., 186, 275-286 (1950). 



«' C. A. Mills, Arch. Biochem., 1, 73-81 (1942). 



68 B. C. Johnson, T. S. Hamilton, and H. H. Mitchell, /. Biol. Chem., 159, 5-8 (1945). 



" R. Busset, Cojnpt. rend. soc. biol , 147, 711-713 (1953). 



'» R. U. Bj-errum and R. E. Wing, /. Biol. Chem., 205, 637-642 (1953). 



" S. Soloway and De W. Stetten, Jr., J. Biol Chem., 204, 207-214 (1953) 



