44G V. CHEMISTRY OF PHOSPHATIDES AND CEREBROSIDES 



(6) Colamine. Although chohne was at first thought to be the nitroge- 

 nous component of cephalin,^^-^^^ it was later shown to be absent from purer 

 preparations of this phosphatide. According to Thierfelder and Klenk/ 

 Baumann, -''•'' and Renall,-''- the identity of the nitrogen-containing com- 

 pound with ethanolamine (colamine) was proved by the experiments of 

 Parnas. The view was then generally accepted that colamine was the sole 

 nitrogenous component of cephalin, and the conflicting evidence of Mac- 

 Arthur^*^ as to the possible acid nature of the compound was largely forgot- 

 ten. Colamine was first separated as an hydrolysis product of bean phos- 

 phatides by Trier^*'* in 1911, although as early as 1884,*'-^ and later in 

 1901,-*''- Thudichum had predicted that this compound would be present in 

 the phosphatides. 



Serine is believed to be the mother substance of colamine. Nord-*^ has 

 suggested that it originates in putrefactive anaerobes, by decarboxylation of 

 serine. 



After the discovery by Folch and Schneider^*^ of the presence of phospha- 

 tidylserine in cephalin preparations, it was suggested that the classical type 

 of cephalin in which colamine is pictured as the nitrogenous base may not 

 actually exist in nature, but that colamine may be an artifact. Such a pos- 

 sibility cannot be overlooked, since phosphatidylethanolamine may con- 

 ceivably originate from phosphatidylserine merely by means of decarboxyl- 

 ation of serine due to postmortem changes in the tissues, or as a result of the 

 analytical procedures employed in its isolation. However, Folch^^ has 

 since shown that such an assumption is erroneous. In the first place, the 

 fatty acid makeup of phosphatidylethanolamine and that of phosphatidyl- 

 serine prepared from the same cephalin are quite different. Whereas the io- 

 dine number of the serine-containing fraction was found to be 33, that for 

 the ethanolamine-containing portion was 78. Phosphatidylserine was iso- 

 lated mostly as the potassium salt, and it contained a large portion of ash, 

 while the phosphatidylethanolamine prepared without acid treatment was 

 largely free from ash. Finally, Folch^^ proved that the postmortem 

 changes were not the cause of the presence of phosphatidylethanolamine, 

 since cephalin, prepared from the brain of an anesthetized animal by imme- 

 diate maceration after removal from the animal, and by mixing with acetone 



»2 H. Cousin, Compt. rend. soc. biol, 62, 238-240 (1907). 



M» C. G. MacArthur, /. Am. Chem. Soc, 36, 2397-2401 (1914). 



2«^ G. Trier, Z. physiol. Chem., 7S, 383-388 (1911). 



*«5 F. F. Nord, Biochem. Z., 95, 281-285 (1919). 



2«« J. Foloh and H, A. Schneider, J. Biol. Chem., 137, 51-62 (1940). 



