135 



receptor mediated processes or non-specific pinocytosis, 

 the rates of pinocytosis of the three cell lines were 



determined. 



125 

 Uptake of I-BSA as a measure of pinocytic capability 



(Chapman-Andresen, 1964; Steinman et al., 1974) showed a 



good correlation of sensitivity to ADH-BSA conjugate and 



pinocytic rate for the three cell lines. AV3 were 3.5 



12 5 

 times more active than CHO cells in the uptake of I-BSA 



whereas EL4 cells were relatively inactive under the same 

 conditions. Pinocytic uptake followed by lysozomal diges- 

 tion of the protein portion of the ADH-BSA (Ehrenreich and 

 Cohn , 1967) with release of free a-amanitin probably contri- 

 butes to the toxicity of the ADH-BSA in susceptible cells. 



ADH-Con A Conjugates 



The preliminary study with ADH-BSA conjugates demon- 

 strated that conjugates of a-amanitin and proteins retain 

 the inhibitory potential of a-amanitin for RNA polymerase 

 II and exhibit differential cytotoxicity for cultured cells. 

 The lack of specific, well defined cellular receptors for 

 the protein portion of the ADH-BSA conjugate made interpre- 

 tation of the cytotoxicity data difficult with respect to spe- 

 cific cell targeting. For this reason, Con A was chosen for 

 conjugation with ADH as a protein carrier with well defined 

 ligand binding and cell receptor specificities. The use of 

 Con A for conjugation studies would also present a readily 

 definable means for assessing the effects of conjugation to 

 a-amanitin on the properties of the carrier protein. 



