cells with high rates of protein uptake, e.g. macrophages, 

 were preferentially killed by conjugated 3-amanitin 



(Barbanti-Brodano and Fiume, 1973; Barbanti-Brodano and 

 Fiume, 1974; Fiume and Barbanti-Brodano, 1974). Further 

 coupling of B-amanitin-albumin conjugates to fluorescein 

 enhanced the conjugate toxicity for hepatocytes, cells 

 known to possess fluorescein receptors (Fiume et al., 1971). 

 Although very qualitative in nature, this work demonstrated 

 that certain conjugates of 3-amanitin were preferentially 

 taken up by cells on the basis of the macromolecular por- 

 tion of the conjugate. Subsequent cell death resulted 

 presumably as a result of transport of the conjugate, or 

 minimally, the amanitin portion to the nucleus where inhi- 

 bition of mRNA synthesis occurred (Faulstich et al., 1975). 

 However, it is likely that the enhanced toxicity of these 

 3-amanitin conjugates is a relatively non-specific phe- 

 nomenon based upon pinocytosis by cells with a high rate 

 of protein uptake. The carbodiimide procedure used for 

 coupling can result in protein cross-linking and ester 

 formation, increasing the molecular weight of the conjugate 

 and decreasing the stability of the linkage (Carraway and 

 Koshland, 1972; Timkovich, 1977). Increased molecular 

 weight and decreased stability of binding of the inhibitor 

 and carrier protein would be apt to favor pinocytic uptake 

 and degradation of the conjugates. 



Other conjugates of 3-amanitin and proteins have been 

 synthesized by formation of the hydroxysuccinimide ester 



