338 ADVENTURES IN RADIOISOTOPE RESEARCH 



liver phosphatides, high values are obtained for the ratio of the specific 

 activity of the brain phosphatide P and the brain inorganic P. Even 

 if v^^e divide these values by 2, to account for the diluting effect of the 

 creatine^^^ P, the resulting figures will still be high. 



Changus, Chaikoff and Ruben<2) observed a progressive increase 

 in the content of radioactive phosphatides in the brain on rats for about 

 200 hours after the administration of labelled phosphorus and it is of 

 interest to note that, in a recent investigation, Chaikoff and his 

 colleagues(3) found that the specific activity of the phosphatide P is not 

 uniform throughout the central nervous system. 



Experiments uith rat 



The specific activity of lecithin P and cephalin P expected from the 

 rat's liver is given in Tables 26 and 27. 



While the ratio of the specific activity of cephalin and lecithin P was 

 found, after 3 hours, to be 1.33, after 24 hours we find the value 0.7. 

 Similarly Chargaff<'*^ found, in experiments taking 24 hours, greater 



Table 26. — Specific Activity of Lecithin 



AND Cephalin in the Rat's Liveb. 



Weight of the rat: 200 gm 



All labelled phosphate was injected subcuta- 



neously at the start of the experiment; 



190 min later, the rat was killed 



turnover figures for lecithin than for cephalin. He found the above ratio 

 to be 0.8. It is also interesting to note that an early paper of Aetom 

 and his colleagues contains data on the relative activity of lecithin and 

 cephalin extracted from the liver of rats to which olive oil and labelled 

 sodium phosphate was administered 9 hours previously. They state the 

 above ratio to be about 0.6. 



(i^ C. Artom, C. Perkier, M. Santangello, G. Sarzana and E. Segre, Arch. 

 Int. Physiol. 45, 35 (1937). 



^2>G. W. Changus, J. L. Chaikoff and S. IIjjbe^, J. Biol. Chem. 126, 493 

 (1938). 



(3) B. A. Fries, G. W. Changus and J. L. Chaikoff, J. Biol. Chem. 132, 24 

 (1940). 



(4>E. Chargaff, ./. liiol. Chem. 128, 592 (1939). 



