448 V. CHEMISTRY OF PHOSPHATIDES AND CEREBROSIDES 



determination of the ammonia set free or by the formaldehyde produced 

 when it reacts with sodium periodate. The ammonia produced is separated 

 by steam distillation by means of a Parnas-Wagner apparatus.-" 



When this procedure is applied to the lipids extracted from tissues, a pre- 

 liminary hydrolysis is carried out with methanolic hydrochloric acid. This 

 is later removed, and the liquid hydrolysate is dissolved in water, extracted 

 with diethyl (or petroleum) ether, filtered, and the ethanolamine and serine 

 are determined on the filtrate. When serine is present, total ammonia is 

 determined on treatment with alkaline periodate before and after adsorp- 

 tion on Permutit. According to Nicolet and Shinn,'-^- serine likewise re- 

 acts quantitatively with periodate. This reaction has been confirmed by 

 Artom.-^" Data obtained from this reaction are in agreement with the re- 

 sults obtained by Van Slyke et alr^^ with another hydroxyamino acid (hy- 

 droxylysine). Jones^^* has proposed still another procedure for the deter- 

 mination of ethanolamine. Burmaster^^^ suggested a micromethod for the 

 determination of ethanolamine in the presence of serine which involves the 

 microdiffusion of ammonia produced by periodate in a solution nearly 

 saturated with potassium metaborate. Special microdiffusion cells made 

 from Petri dishes are required for the latter determination. 



(3) Phosphatidylserine 



The fact that the phosphatides might contain an amino acid residue was 

 first suggested by Mac Arthur. ^^^ He based this assumption upon the 

 demonstration of the solubilizing effect of cephalin upon copper obtained 

 from cupric hydroxide. This is the same reaction upon which the Kober- 

 Sugiura method^^^ for the determination of amino acids is based. How- 

 ever, because of the non-specificity of the latter method, and because of the 

 proof by other workers of the presence of ethanolamine in cephalin, little at- 

 tention was paid to MacArthur's results until recently. 



The proof that cephalin may contain an amino acid fraction has recently 

 been brought forward by Folch and Schneider. ^^^ These investigators 

 found that four different presumably pure samples of brain cephalin, which 

 possessed the constants usually accepted for this phosphatide, all gave val- 

 ues for amino nitrogen when analyzed by the ninhydrin-carbon dioxide 

 method slightly modified from that of Van Slyke and Dillon. -^^ Only a- 



2" J. K. Pamas and R. Wagner, Biochem. Z., 125, 253-256 (1921). 

 232 B. H. Nicolet and L. A. Shinn, /. Biol. Chem., 139, 687-692 (1941). 

 2" D. D. Van Slvke, A. Hiller, and D. A. MacFadyen, /. Biol. Chem., I4I, 681-705 

 (1941). 



"* J. H. Jones, J. Assoc. Official Agr. Chem., 27, 462-467 (1944). 



295 C. F. Burmaster, /. Biol. Chem., 165, 1-6 (1946). 



296 P. A. Kober and K. Sugiura, J. Am. Chem. Soc, 35, 1546-1584 (1913). 



297 D. D. Van Slyke and R. T. Dillon, Compt. rend. trav. lab. Carlsberg, Ser. chim., 22, 

 480-486 (1938). 



