43.S V. CHEMISTRY OF P?IOSPHATIDES AND CEREBROSIDES 



e. Phosphorylcholine. Phosphorylcholine is one of the substances 

 formed by the action of lecithinase D on lecithin. Although there is no 

 proof that such an enzyme occurs in animal tissues, it has been noted earlier 

 that it is present in the gas bacillus {Clostridium welchii). Phosphoryl- 

 choline may play an important role in intermediary metabolism, as is indi- 

 cated by Taurog's-^^ demonstration that an incorporation of P-*- from phos- 

 phorylcholine into both kidney and liver phospholipid occurs in vivo. 

 Riley-^^ has also proved that phosphorylcholine disappears rapidly from the 

 blood stream when it is injected, and appears as an inorganic phosphate in 

 the blood. 



HO /CH3 



0=P-0-CH2CH2N— CHj 



HO I^CH, 



OH ' 



Phosphorylcholine 



Phosphorjdcholine is resistant to acid hydrolysis, in contrast to the be- 

 havior of lecithin and of other choline esters. 2*°'^*^ This hydrolysis has been 

 found to follow a pseudo-unimolecular reaction [ki^^io = 1.16 X 10~'].^" 

 However, although only an insignificant hydrolysis does occur in acid at 

 100°C., the fact that hydrolysis results at 125°C. leads Baer and McAr- 

 thur^^'' to the conclusion that it should be included in the same class as a- 

 glycerophosphoric acid, |S-glycerophosphoric acid, and glyceric acid-3-phos- 

 phoric acid, insofar as stability toward acid is concerned. It has been sug- 

 gested that the stability of phosphorylcholine to acid is due to the fact that 

 it is a mono-ester of phosphoric acid.^" 



Phosphorylcholine is also extremely resistant to alkaline hydrolysis. It 

 is not saponified by heating at 100°C. for 100 hours with 2 N alkali nor with 

 10 A'' alkali for 30 minutes at 118-120°C. However, on raising the saponi- 

 fication temperature to 125°C. and extending the period to 50 hours, Baer 

 and McArthur were able to demonstrate a 40% hydrolysis. Many side re- 

 actions occur which result in the destruction of the free ester or of the cho- 

 line. Although phosphatase hydrolyzes phosphorylcholine,^^" it is not split 

 by true choline esterase or by pseudocholine esterase. It is suggested that 

 it may play a more important role in phosphate metabolism than it does in 

 the intermediary metabolism of choline. 



Phosphorylcholine can be readily synthesized by a number of procedures. 

 These include phosphorylation of choline halide with POCls^'*"-^*- 



^^ A. Taurog, Unpublished experiments, reported bj^ I. L. Chaikoff, Phijsiol. Revs., SS, 

 310 (1942). 



"9 R. F. Riley, J. Biol. Chem., 153, 535-549 (1944). 



»« R. H. A. Plimmer and W. J. N. Burch, Biochem. J., 31, 398-409 (1937). 



"1 A. B. L. Bezndk and E. Chain, Quart. J. Exptl. Physiol. 26, 201-214 (193G-1937). 



2« E. Schmidt, Ann., 337, 37-121 (1904). 



