absorbed to Sephadex G-75 and eluted with specific sac- 

 charide in volumes identical to native Con A. The conju- 

 gates agglutinated red blood cells at near equivalent con- 

 centrations to Con A. Evidence from other Con A conjugates 

 substituted with hippuric acid as an analog for ADGG indi- 

 cate that the ADGG-Con A conjugates retain full lectin 

 associated ligand binding specificities. 



Exposure of H-7 CHO cells for short periods of time 

 to ADGG-Con A resulted in 50% inhibition of cell prolifer- 

 ation at 2.1 x 10 M with respect to ADGG concentration. 

 At that concentration, free ADGG or the equivalent amount 

 of Con A to that present in the conjugate had no effect. 

 Extrapolation from the maximum doses of ADGG used indicates 

 that a minimum 50-fold enhancement of the toxicity of free 

 ADGG is achieved by conjugation to Con A. Cell binding 



measurements determined that ADGG-Con A is bound by H-7 



125 

 CHO cells in identical amounts to I-Con A, that it 



125 

 competes for I-Con A binding sites as efficiently as 



native Con A, and that its binding is inhibitable by pre- 

 incubation of cells with Con A or by the presence of the 

 Con A specific ligand, a-methyl-D-mannopyranoside (MDM) . 

 The potent toxicity of ADGG-Con A for H-7 CHO was abolished 

 by treatment of the conjugate with MDM prior to exposure 

 of the cells. These data strongly suggest that ADGG-Con A 

 conjugates derive their enhanced toxicity for CHO cells 

 from the binding to specific cell receptors with subsequent 

 internalization of the bound a-amanitin. Confirmation of 



v 



