232 



TORE HULTIN et al. 



behind the activation effects described. It may be recalled from the 

 previous section that unexpectedly high incorporation values were often 

 obtained in systems containing mitochondria-free liver homogenates from 

 animals treated with sublethal doses of phalloidin (Fig. 4). This effect 

 could be related to a characteristic modification of the normal time course 

 of the incorporation. In liver systems from animals recovering after amino- 

 fluorene treatment the maximal rate of incorporation may possibly be 

 reached slightly earlier than usual (Fig. 5), but the quantitative importance 



300 



CM 



E 



E 200 



Q. 



100- 



A 8 12 0^8 



minutes of i ncubat ion 



Fig. 5. Incorporation of [^*C]-L-leucine into protein by mitochondria-free 

 guinea-pig liver homogenates. At zero time, or after 4 or 8 min. of incubation 

 (35 C) o -08 /nmole of [^''C]-L-leucine, 10 /^^moles of PEP and i /xmole of ATP were 

 added. Incubation was interrupted 4 min. later by the addition of TCA. Open 

 bars: control livers. Solid bars: livers from animals given 2-aminofluorene (2-5 

 mmoles/kg.) 21 hr. prior to decapitation. 



of this tendency must be fairly limited. As is evident from the time-course 

 curve shown in Fig. i, stimulation effects of the kind discussed here could 

 in principle be due to a prolongation of the active life-span of the micro- 

 somes. However, with the liver preparations from the aminofluorene- 

 treated animals there was no indication of any appreciably longer active 

 period. As is shown by Fig. 5, the increase in incorporation activity was 

 equally pronounced in the period with maximal incorporation rate as in 

 any other incubation period. 



In cell-free liver systems from adult animals only a limited part of in- 

 corporated, labelled amino acids becomes distributed to the proteins of 



