PHOSPHOLIPIDS 53 



by the use of radiophosphate in the medium. Simultaneously with the 

 formation of new phospholipid, catabolism of the phospholipid formed was 

 shown to occur. The net result was a decline in total liver phospholipid, 

 while phosphohpid P^^ was being laid down. Taurog et al^^^ reported 

 that oxygen was required for the maintenance of the synthetic reaction, 

 while it was inhibited to the extent of 90% when cyanide or hydrogen sul- 

 phide was present, and under anaerobic conditions. The state of tissue 

 organization was also found to be important in the in vitro synthesis of phos- 

 pholipids; the abihty to effect phospholipid synthesis was completely lost 

 in liver homogenates.^** On the other hand, Ackerman and co-workers^^^ 

 were unable to demonstrate the synthesis of phospholipid in rat liver 

 shces, incubated with L-methionine and 2-dimethylaminoethanol, unless 

 the activity of choline oxidase was inhibited with KCN. Under the latter 

 condition, a net synthesis of 0.2 to 0.6 mg. of choline per g. of liver could be 

 observed. In the absence of an inhibitor, choline was oxidized to betaine 

 before it could be incorporated into the phospholipid molecule. 



b. Intestine. The intestine offers a second site for the synthesis of 

 phospholipids. Thus, it has been demonstrated that phospholipid con- 

 taining P^- is rapidly deposited in the gastrointestinal tract after the ad- 

 ministration of phosphate containing isotopic p. 237,245-247,250,251 Yvie^ et al.^^° 

 reported that the small intestine is much more active in effecting phos- 

 phorylation than is the stomach or the large intestine. Similar variations 

 in phosphohpid synthesis have been noted in different parts of the gastro- 

 intestinal tract of birds. The greatest rate of synthesis was noted in the 

 small intestine; this level exceeded that in the gizzard, proventiculus, ce- 

 cum, and colon. 2^^ When the P*^ was given orally, the specific activity 

 of phospholipid P^^ in the intestine was shown to exceed that in the liver. ^^^ 

 Proof that the route of administration is concerned with the high activity 

 noted in the intestine is furnished by the fact that a higher value for in- 

 testine phospholipid P^^ was noted when the labeled inorganic phosphate 

 was given orally than when it was administered subcutaneously.^^" In 

 harmony with the results on the liver, the incorporation of P*^ occurs 

 more rapidly in the cephahn fraction than in that of lecithin during the 

 first four hours ;^" however, at longer intervals, the situation is reversed. ^^^ 



c. Kidney. Considerable evidence exists that the kidney is likewise able 

 to effect a synthesis of phospholipid. However, Artom et al.^^^ and Perl- 

 man and associates'''^ are in agreement that the rate of phospholipid syn- 

 thesis is slower in the kidney than in the small intestine or liver. More- 



«« A. Taurog, I. L. Chaikoff, and I. Perlman, /. Biol. Chem., 145, 281-291 (1942). 



^'' C. J. Ackerman, M. J. Burns, and W. D. Salmon, Federation Proc., 12, 165 (1953). 



