AMINO ACID INCORPORATION BY LIVER MICROSOMES 



223 



system with whole microsomes and that with isolated RNP-particles : 

 With the isolated particles there was a considerably longer period of active 

 incorporation. 



1000 



Period of preincubation, minutes 



Fig. I. Life-span of incorporation systems with microsomes or RNP-particles 

 from rat liver. • RNP-particles and cell sap [26]. A Microsomes and cell sap (mito- 

 chondria-free homogenate) [5]. At the indicated periods of incubation (35 ) the 

 following components were added: o-o8 /xmole [^^CJ-L-leucine (5 75 mC/mmole), 

 10 /xmoles PEP, i /xmole ATP and 0-2 /xmole GTP. Final volumes i o ml. Incuba- 

 tion period after these additions 15 min. Proteins were purified and counted as 

 described previously [5]. 



Effects of liver poisons on the activity of microsome systems 



The tendency of the membrane fragments of liver microsomes to exert 

 an unfavourable influence on the incorporation activity becomes con- 

 siderably more pronounced in experiments with liver preparations from 

 certain kinds of pretreated animals. The experiment illustrated by Fig. 2 

 [8] was carried out with liver microsomes from guinea-pigs which had 

 been treated for 2 hr. with the liver poison phalloidin [32] (0-5 /xg./kg., 

 intravenous injection). The activity of these microsomes in amino acid in- 

 corporation was determined at a series of increasing concentrations by use 

 of a standard assay system containing excess amounts of soluble fraction 

 from normal guinea-pig liver. Incubation tubes with microsomes from 

 normal guinea-pig liver at the same concentrations were run in parallel. 



