PHOSPHOLIPIDS 59 



the fact that bone marrow is capable of synthesizing phosphohpids, as 

 demonstrated by in vitro tests as well as by in vivo experiments, is con- 

 vincing evidence of the independent synthesis in the bone marrow. 



j. Neoplastic Tissue. The rate at which phospholipid formation 

 occurs in malignant tissue has been shown to be high, resembling that in 

 normal liver, kidney, or small intestine. ^^^-^^^'^^^ However, in contradis- 

 tinction to the behavior of tissues from normal animals, the maximal dep- 

 osition of P*- in phospholipid may last as long as forty to fifty hours. 

 The turnover rates of lecithin in rat carcinosarcoma 256 were reported to be 

 somewhat higher than those of cephalin.^^^ Moreover, the rate of incor- 

 poration of P^^ into phospholipids varies with the type of tumor. Thus, 

 Jones et aL-'*^-^^* reported that lymphosarcomas and mammary carcinomas 

 are much more active than is sarcoma 180 or lymphoma. 



(5) Factors Affecting the Biosynthesis of Phospholipids 



In addition to the factors already discussed, such as tissue and age, a 

 number of more general conditions are concerned with the rate of syn- 

 thesis of phospholipids. 



a. The Effect of Diet. The presence of fat in the gastrointestinal tract 

 has been shown to increase phospholipid synthesis in the small intestine. ^^^ 

 Moreover, an increased phospholipid turnover was found to be associated 

 with the action of choline in sweeping out fat from the liver of rats on a 

 high-fat diet. 2^^ However, in the case of the liver, the ratio of phosphohpid 

 P to N was found to be constant irrespective of the protein or fat content 

 of the diet, or whether or not the liver was normal, fatty, or fibrotic.^^" 

 The same constancy in the ratio of phospholipid to nucleoprotein syn- 

 thesized in the liver Avas also shown by Cornatzer et al}^^ to exist under a 

 mde variety of conditions. However, Campbell and Kosterlitz^^^ found 

 that, whereas the desoxyribonucleic acid content of the liver, and its turn- 

 over in rats, are not affected by variations in the protein, fat, or choline 

 content of the diet, the phosphohpid P content is determined mainly by pro- 

 tein intake, to a small extent by the dietary fat, and not to any degree by 

 the choline in the diet. The ratio of phosphohpid P: protein N was 

 found to be constant over a wide range of protein intake. The only situ- 



28* F. L. Haven, /. Nat. Cancer Inst., 1, 205-209 (1940). 



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



"0 W. E. Cornatzer, J. P. Davison, and D. G. Gallo, Federation Proc, 12, 191-192 

 (1953). 



"^ W. E. Cornatzer, D. G. Gallo, and J. P. Davison, XIX Intern. Physiol. Congr., 

 Montreal, Aug.-Sept., 1953, Abst., 282-283. 



"" R. M. Campbell and H. W. Kosterlitz, Biochim. et Biophys. Acta, 8, 664-679 (1952). 



