56 II. BIOSYNTHESIS 



Fries and Chaikoff"^ reported that the highest P*^ recovery in all divisions 

 of the central nervous system was on the day of birth. However, the age 

 at which the maximum turnover rate of the brain phospholipids was ob- 

 served varied in the different parts of the central nervous system. ^^^ Dur- 

 ing the period from birth until the rat reached the weight of 50 g. phospho- 

 lipid activity was highest in the spinal cord, after which the relative ac- 

 tivity of the forebrain, cerebellum, and medulla increased steadily. By the 

 time the animals had attained weights of 200 or 300 g., the phospholipid 

 turnover in these tissues sometimes exceeded that in the cord.^^^-"^ 



The synthesis of phospholipid in the brain is influenced by the degree 

 of activity. Thus, Torda^'''' reported that convulsive agents, such as 

 pentylene tetrazole, physostigmine salicylate, or electro-shock, signifi- 

 cantly reduced the specific activity of brain phospholipids. On the other 

 hand, the administration of adrenocorticotropin (ACTH) restored the 

 synthetic capacity of the brain to form phosphoUpids. This indicates that 

 the phospholipid turnover is influenced by hormones. 



The earlier observations on the intact animal do not indicate whether or 

 not brain tissue possesses the capacity to synthesize phospholipids per se. 

 The answer to this problem has been arrived at by the use of technics 

 similar to those employed to prove this point in the case of other tissues. 

 Thus, on the basis of in vitro tests. Fries and co-workers^^^ showed that sur- 

 viving brain slices were able to incorporate P^^ into phospholipids when 

 the slices were immersed in a Ringer-bicarbonate solution containing radio- 

 active phosphate. Brain homogenates were able to synthesize phospho- 

 lipids, although the rate was slower than in the organized tissues such as 

 shces. Dawson"^ found that the rate of synthesis of phospholipids in the 

 brain homogenates from guinea pigs was dependent upon the extent of 

 oxidative phosphorylation, and was controlled by it. Moreover, the 

 phospholipids synthesized were confined to certain components of the 

 cephalin fraction (phosphatidylserine and diphosphoinositide), while 

 practically no new formation of lecithins, sphingomyelm, or phosphatidyl- 

 ethanolamine could be observed. 



In contradistinction to the activity of homogenates of the brain in ef- 

 fecting syntheses,-^" those from the liver are entirely inactive in the syn- 

 thesis of phospholipids, although the slices of the latter organ are very 

 effective in promoting this reaction. ^^^ The rate of phospholipid synthesis 



276 B. A. Fries, G. W. Changus, and I. L. Chaikoff, /. Biol. Chem., 132, 23-34 (1940). 



2" C. Torda, Federation Proc, 12, 145 (1953). 



278 B. A. Fries, H. Schachner, and I. L. Chaikoff, /. Biol. Chem., 144, 59-66 (1942). 



2" R. M. C. Dawson, Biochem. J., 53, viii (1953). 



280 H. Schachner, B. A. Fries, and I. L. Chaikoff, /. Biol. Chem., I46, 95-103 (1942). 



