198 



L. A. STOCKEN 



is left in the dead rat for a short time the ATP content decUnes. This 

 of course is not unexpected but it is of interest that the bound inorganic 

 phosphate increases roughly in an inverse ratio. Allfrey et al. (lOSTb) 

 have pointed out that the phosphorylation of mononucleotide is not 

 effected by extranuclear inorganic phosphate and with this we are in 

 agreement. 



We have carried out some experiments with thymus nuclei from rats 

 killed at various times post injection of 32p. The rather surprising 

 finding is that the bound inorganic phosphate of the nuclei has a 

 markedly higher specific activity than any other cell fraction. This 



Table II. Specific activities of acid-soluble 'phosphates in red thymus after 

 injecting 50 /<C ^^p intramuscularly I lOOg body iveight 



Specific activity as counts jjer min per /ng P (SA) 



may be due to differences in accessibility of organo-phosphates in 

 different cell compartments to enzymic hydrolysis. 



Data for mitochondria are less easy to obtain since two separate pre- 

 parations have to be made to obtain nuclei and mitochondria. Experi- 

 ments in vitro showed that the bound Pi was exchangeable with added 

 Pi and incubation of radioactive nuclei with inert Pi or of inactive 

 nuclei with 32pj^ shows the expected changes in specific activity. 



We have lately been preoccupied to find a more controlled system 

 for the study of penetration of ions to the nucleus and preliminary 

 experiments indicate that a suspension of isolated thymocytes will 

 prove useful. 



