18 CHOLINE 



C. MECHANISM OF ACTION OF CHOLINE 



1. Derivatives of Phosphorylcholine 



In so far as participation in the intermediary metabolism of phospho- 

 lipids is concerned, it is important to determine the relative activities of 

 choline and its phosphorylated derivatives. Of these phosphorylcholine and 

 glycerylphosphorylcholine (GPC) have received special attention. Riley 

 determined the rate of utilization of radioactive phosphorylcholine (P^^) in 

 rats and found no evidence of its preferential use in phospholipid metabo- 

 lism^^ or in bone metabolism.^^ Severe choline deficiency did not alter the 

 uptake of P^^ by the femur to any marked degree.*" Schmidt et al.^^ have 



TABLE II 



Amounts of Free Choline and of Glycerylphosphorylcholine (GPC) in Some 



Mammalian Tissues^^ 



analyzed tissues for free choline and GPC and have made the surprising 

 observation that GPC may make up a relatively large fraction of the total 

 free and combined tissue choline. This was true particularly in lamb liver 

 whereas beef and rat livers contained only negligible quantities of either 

 free choline or GPC (Table II). The incubation of ground beef pancreas 

 increased free choline slightly and GPC markedly. Neither compound oc- 

 curred in rat intestine in more than traces, but incubation of ground intes- 

 tine at pH 5.2 resulted in liberation of GPC whereas incubation at pH 8.2 

 yielded free choline. Schmidt et al. believe that their findings suggest the 



28 R. F. Riley, J. Biol. Chem. 153, 535 (1944). 



23 R. F. Riley, B. McCleary, and R. E. Johnson, Am. J. Physiol. 143, 677 (1945). 

 30 W. F. Neuman and R. F. Riley, /. Biol. Chem. 168, 545 (1947). 

 5' G. Schmidt, L. Hecht, P. Fallot, L. Greenbaum, and S. J. Thannhauser, /. Biol. 

 Chem. 197, 601 (1952). 



