LIPID STORAGE UNDER ABNORMAL CONDITIONS 663 



aZ., 729 and others 722 - 723 to be lipotropic, 717 and it has been proved that it does 

 not furnish labile methyl groups. 652 This latter compound must act by 

 being incorporated into the phospholipid molecule, although Channon et 

 al. 730 were unable to detect it in the liver phospholipids under such circum- 

 stances. McArthur and co-workers 729 reported significant differences be- 

 tween the microchemical and the microbiological assays for choline in the 

 hydrolysates of the phospholipids isolated from the livers of rats fed tri- 

 ethylcholine. Subsequently these workers were able to fractionate the 

 phospholipids and to obtain chemical proof that the triethyl homologue 

 had been incorporated in the phospholipid molecule. 



The importance of choline in the synthesis of phospholipids is likewise 

 shown by its effect on the rate of turnover of this component. When 

 choline was fed, the half-life of phosphatide choline was found by Boxer 

 and Stetten 731 to be six days, with a daily replacement of choline in the 

 phospholipids amounting to 3.9 mg. per rat per day. On the other hand, 

 when no choline was fed, the half-life of choline was increased to eighteen 

 days, and the daily replacement of choline in the phospholipids was reduced 

 to 1.3 mg. daily. Although the total quantity of choline in such phos- 

 pholipids was not influenced by choline-free diets, the rate of the inter- 

 change was profoundly affected. 



Further evidence that choline plays a role in phospholipid synthesis was 

 brought forward by Perlman and Chaikoff, 732 and by Perlman et al., 133 who 

 based their conclusions upon the use of P 32 . These workers showed that an 

 increased formation and a more rapid removal of phospholipids occurred in 

 the livers of rats fed choline, as compared with those which did not receive 

 this compound. The effect of a single dose of ingested choline was noted 

 within one hour, and its effect was dissipated within ten to twelve hours. 

 Moreover, the increase in phospholipid was found to be proportional to the 

 amount of choline administered. In the experiments of Horning and 

 Eckstein, 734 the lipotropic action of methionine and of choline could be 

 demonstrated within eight hours after their ingestion. Using P 32 , they 

 found that an increased transport of radiophosphorus to the liver phos- 

 pholipids occurred. This was not invariably associated with a decrease in 

 liver lipids, and may not be related to it. Cornatzer and Cayer 735 report 



729 C. S. McArthur, C. C. Lucas, and C. H. Best, Biochem. J., 41, 612-618 (1947). 



730 H. J. Channon, A. P. Piatt, J. V. Loach, and J. A. B. Smith, Biochem. J., 31, 2181- 

 2186(1937). 



731 G. E. Boxer and De W. Stetten, Jr., J. Biol. Chem., 153, 617-625 (1944). 



732 I. Perlman and I. L. Chaikoff, /. Biol. Chem., 127, 211-220 (1939). 



733 I. Perlman, N. Stillman, and I. L. Chaikoff, J. Biol. Chem., 133, 651-659 (1940). 



734 M. G. Horning and H. C. Eckstein, J. Biol. Chem., 166, 711-720 (1946). 

 736 W. E. Cornatzer and D. Cayer, J. Clin. Invest., 29, 542-551 (1950). 



