228 



TORE HULTIN et ol. 



It may be relevant in this connection to mention some characteristic 

 properties of cell-free incorporation systems containing mitochondria-free 

 homogenates from liver [7]. Contrary to what would reasonably be 

 expected in view of the limited life-span of these systems, the incorporation 

 rate is not optimal just after the beginning of the incubation, but attains 

 a fairly distinct maximum after some period of preincubation, the duration 

 of which varies with temperature (Fig. 3). This lag is not due to the time 



400 



E 



E 



Q. 



200 



Time in minutes 



Fig. 4. Amino acid incorporation by mitochondria-free liver homogenates 

 from normal {a) and phalloidin-treated (h, c) guinea-pigs. Doses of phalloidin 

 0-4-0 -5 /xg./kg. System as in Fig. i. [^*C]-L-leucine was added at the indicated 

 periods of incubation, and TCA at 15 min. (35'). 



required for the labelled amino acids to become activated, since in the 

 illustrated experiment the nucleoside triphosphate-generating system was 

 added to the system together with the labelled amino acid at the different 

 periods indicated. 



When mitochondria-free homogenates were prepared from phalloidin- 

 treated mice or guinea-pigs, the preincubation effect was less pronounced 

 or absent. The incorporation then proceeded at a maximal rate from the 

 beginning of the incubation. With animals treated with small doses of 

 phalloidin the paradoxical situation therefore sometimes occurred that 

 over a 15 min. incubation period the total incorporation became higher in 

 liver homogenates from the phalloidin-treated animals than in those from 

 the controls (Fig. 4). 



