52 II. BIOSYNTHESIS 



lipid synthesis likewise occurred in rats deprived of kidneys and gastroin- 

 testinal tract but with intact livers.-^" 



When the rate of turnover of phospholipids in the liver was determined 

 by the procedure of Hevesy and Hahn,^*^ it was calculated that 19% of 

 the total phospholipid in the liver was renewed within four hours. Ac- 

 cording to the data of Chargaff, alone and with co-workers,^^^-^^^ the rate 

 of lecithin formation in the hver exceeds that of cephalin. Although 

 similar results were obtained in experiments in which the time interval 

 exceeded one day, Hevesy and Hahn-" noted that the cephalin turnover 

 occurred more rapidly in the four-hour tests. Hunter^^* reported that 

 sphingomyelin accounted for only a small fraction of the new liver phos- 

 pholipid formed, as determined by the use of P^^. 



The administration of choline was found by Entenman and co-workers^^* 

 to increase the rate of synthesis and turnover of the choline-containing 

 phospholipids in the liver of the dog; on the other hand, the specific ac- 

 tivity of the non-choline-containing phospholipids was not increased, but 

 was actually depressed. According to the report of Stekol et al.,^*^ differ- 

 ences can be noted in the utilization of the methyl group from methionine 

 and from choline for phospholipid synthesis. After methionine-C^^Hs was 

 injected, the period of decreasing choline-C^^ content in the hver was ac- 

 companied by a simultaneous increase in carcass choline-C^'^Hs up to 240 

 hours. When choline-C^^Hs itself was injected, the gradual decrease of 

 choline-C^* in the liver was not associated with a concomitant increase in 

 tissue choline. However, the level of choline reached in the carcass fol- 

 lowing the injection of choline was considerably higher than that after 

 methionine had been administered. The authors suggest that, although 

 there is no doubt about the chemical identity of the choline-C* 

 in the phospholipids formed after the administration of choline or 

 methionine, there is a possibility of the nonidentity of the phospholipid 

 molecules into which the intact choline-C^* or the choline synthesized from 

 methionine-C^^ enter. 



Fishier and associates'^* were the first to demonstrate the in vitro forma- 

 tion of phospholipids in liver slices, a finding which was rendered possible 



260 B. A. Fries, S. Ruben, I. Perlman, and I. L. Chaikoff, /. Biol. Chem., 123, 587-593 

 (1938). , 



2" E. Chargaflf, /. Biol. Chem., 128, 587-595 (1939). I 



2" E. Chargaff, K. B. Olson, and P. F. Partington, /. Biol. Chem., 134, 505-514 (1940). 



2" F. E. Hunter, Proc. Soc. Exptl. Biol. Med., 46, 281-282 (1941). 



2" C. Entenman, I. L. Chaikoff, and H. D. Friedlander, /. Biol. Chem., 162, 111-118 

 (1946). 



256 M. C. Fishier, A. Taurog, I. Perlman, and I. L. Chaikoff, J. Biol. Chem., I4I, 809- 

 818(1941). 



