Studies on the Mechanism of Protein Synthesis 165 



mouse ascites tumour cells. Here it is possible to obtain good 

 incorporation into the ribonucleoprotein particulate fraction 

 of the microsomes, in the almost complete absence of the mem- 

 branous lipoprotein fraction. While these two fractions of the 

 microsome pellet can also be separated by means of sodium 



HOMOGENIZATION in 2.5 volumes of medium A 



I5,000x^ lOmin. 



ppt. (discard) 

 SUPERNATANT 



+ 3 volumes of medium B 



105,000 x^ 60 min, 



microsome pellet 

 SUPERNATANT 



+ I volume of medium B 



pH to 5.2 and then centrifuge 



Supernatant 

 (discard) 



PRECIPITATE 



Supernatant 

 (discard) 



Resuspend in same volume 

 of medium B and 

 centrifuge. 



Fig. 1. Fractionation scheme for rat liver. 

 Medium A: 0-35 m sucrose, 035 M-KHCO3, 004 M-MgCla, 025 m-KCI. 

 Medium B: 0-9 m sucrose, 004 M-MgClg, 025 m-KCI. 



deoxycholate, after such treatment the ribonucleoprotein 

 particles are biologically inactive, presumably due to denatur- 

 ation. This newer separation method is a gentler procedure, 

 which preserves the fragile synthetic activity of this particle. 

 Another advantage in using cellular fractions from the 

 mouse ascites tumour is that 10 (jlm of ATP per ml. in itself is 

 adequate for energy generation, and the ATP regenerating 



