143 



H-7Wcr cells were unaffected by a 15 minute exposure 



to Con A as was expected. They were, however, very sensitive 



to ADGG-Con A with an ID cn of 3.5 x 10~ 7 M (Table 9). This 



bU 



value is comparable to that seen with H-7 cells and indi- 

 cates that either H-7Wcr cells are resistant to the effects 

 of Con A at a step after internalization of bound Con A or 

 that ADGG-Con A is degraded on the cell surface with entry 

 to the cell of only the amanitin portion of the conjugate. 



In contrast to the effects seen on H-7 cells, free 

 a-amanitin and ADGG did inhibit the H-7Wcr cells following 

 a 15 minute exposure, although, at the maximum dose tested 

 of 2 x 10 M neither inhibitor produced half the inhibition 

 seen with ADGG-Con A. A likely explanation is that the 

 mechanism of the H-7Wcr resistance to Con A involves alter- 

 ations in membrane components that allow for rapid entry 

 of the unconjugated inhibitors. If this is the case, the 

 entry must be saturable with respect to amanitin as the con- 

 tinuous exposure data indicate that no more of either com- 

 pound enters the H-7Wcr cell than enters the H-7 cell. The 



rapid plateauing of the 15 minute inhibition data after 



— fi 

 exposure to a 0.5 x 10 M concentration of both ADGG and a- 



amanitin supports this hypothesis. 



In order to establish that the inhibition caused by 



ADGG-Con A conjugate is a function of the inhibition of 



RNA polymerase II by the amanitin portion of the conjugate, 



the toxicity of ADGG-Con A was examined in a cell line 



resistant to a-amanitin. LAN-2 cells possess an altered 



