226 TORE HULTIN et al. 



TABLE III 



Effect of Phalloidin-Treatment in vivo on the ATP-Breakdown in Incor- 

 poration Systems with Guinea-Pig Liver Microsomes 



Release of orthophosphate from ATP (ii ^moles) or ATP (i /xmole) and PEP 

 (lo /^moles) in incorporation systems containing liver microsomes from control 

 and phalloidin-treated guinea-pigs. Incubation system otherwise as in Fig. 2. 

 ATPase activity [19] of the control liver microsomes: i 5 jumoles orthophosphate/ 

 15 min./mg. microsomal protein. 



/xmoles Pj formed in 15 min. 



per mg. microsomal protein /o Inhibition 

 of ["C]-L-leucine 



I umole ATP + , . rr.T^ incorporation 



1 T^T-T^ 1 1 umoles A 1 P 



10 /Limoles PEP 



Control liver 2 • 6 3 • i 



Phalloidin liver 1-9 20 



observed in the presence of microsomes from phalloidin-treated guinea- 



Effects of a somewhat similar kind have been obtained in rat liver with 

 the liver carcinogen, dimethylnitrosamine [12, 13], and to some extent 

 also with 2-aminofluorene [i]. Taken together these experiments indicate 

 that the incorporation in vitro of amino acids into protein by liver micro- 

 somes is influenced by factors acting in the membrane components of the 

 microsomes. Such factors may be predetermined by conditions prevailing 

 already in the living cells. 



Evidence of stimulation effects in cell-free systems 



The experiments discussed above serve to illustrate the fact that 

 under certain conditions the activity of cell-free incorporation systems 

 may be abnormally low in proportion to their content of microsomal RNA, 

 owing to the influence of factors induced already in vivo. 



The opposite situation may also be met with in the study of cell-free 

 systems of this type, i.e. that the incorporation activity shows a marked 

 enhancement which cannot be explained on the basis of a proportional 

 increase in the total content of RNP-particles. The first observation of 

 this kind was made in sea urchin eggs in connection with their fertilization 

 [14]. Only a few minutes after fertilization when the total number of 

 RNP-particles still must have been very nearly the same as in the un- 

 fertilized eggs, the activity of whole egg homogenates in amino acid in- 

 corporation was considerably increased (Table IV). The same was true 

 with "mitochondria-free homogenates" (centrifuged for 8 min. at 12 000 

 X g). The fertilization reaction rapidly seemed to make the individual 

 RNP-particles more active in amino acid incorporation, in such manner 



