AMINO ACID INCORPORATION BY LIVER MICROSOMES 229 



Stimulation effects in liver systems with relationship to the action 



of cortisone 



As was briefly mentioned in a previous section the treatment of rats 

 with Hver carcinogens may lead to a reduced activity of the isolated micro- 

 somes in amino acid incorporation. After a single dose of 2-aminofluorene 

 (2-5 mmoles per kg.) this effect is usually observed most easily 4-6 hr. 

 after the administration. 



Only a few hours later a strikingly different picture develops. As is 

 shown by Table V, 20 hr. after the administration of 2-aminofluorene the 



TABLE V 



Effect of in vivo Treatment with 2-Aminofluorene (AF) or z-Aminoaphtha- 



LENE (AN) ON THE INCORPORATION OF [1^C]-L-LeUCINE INTO PrOTEIN BY CeLL- 



Free Liver Systems 



The carcinogens (2-5 mmoles /kg. body weight) were administered 21 hr. 

 prior to sacrifice. Incorporation system as in Fig. i. Incubation period (35°) 10 min. 



* RNA /protein ratio 120 per cent of that of normal homogenate [3]. 

 t Primary values expressed as c. p.m. /cm-, per 100 /xg. of particle-bound RNA 

 added to system (cf. Fig. 2). 



activity of mitochondria-free rat liver homogenates in amino acid incorpora- 

 tion was increased far above the normal level. At the same time there was 

 some increase of the RNA-content in the homogenates, but this increase 

 (usually less than 25%) was not nearly so great as the sometimes several- 

 fold rise in incorporation activity. 



Owing to the lack of proportionality between the activity of these liver 

 homogenates in amino acid incorporation and their RNA contents it 

 seemed possible that the activity increase might depend on a more eflicient 

 amino acid activation. It turned out, however, that this was not the main 

 reason of the effect. Liver microsomes were prepared in parallel from 

 aminofluorene-treated and normal rats and their incorporation activities 

 were determined at different concentrations in a system containing standard 

 amounts of normal soluble liver fraction. The microsomal activities were 

 then compared at equal RNA or protein concentrations in the same way as 

 in the phalloidin experiments described before. As is shown in Table V 



