145 

 The remaining evidence necessary for confirmation of 



the above mechanism is to establish that ADGG-Con A does 



indeed bind to cells via specific receptors for Con A. 



The binding of ADGG-Con A by H-7 CHO cells was determined 



3 

 directly with H-DM-ADGG-Con A and compared with the results 



obtained with equivalent amounts of I-Con A. At 2 x 10 M 

 with respect to Con A concentration, H-7 cells bound identi- 

 cal amounts of either Con A derivative (Table 7). The 

 binding of each substance was equally inhibited by pre- 

 incubation with excess unlabeled Con A. Exposure in the 



- 3 125 



presence of 10 M MDM resulted in 85% inhibition of I- 



3 

 Con A binding and 76% inhibition of H-DM-ADGG-Con A binding. 



These results indicate that essentially identical numbers 



of Con A and ADGG-Con A molecules are bound by H-7 CHO cells 



and that they have the same apparent specificities of binding. 



A more direct comparison was made by competition of native 



125 

 Con A and ADGG-Con A with I-Con A for receptor sites pre- 

 sent on H-7 cells (Figure 25). The results, when plotted as 



125 

 fraction I-Con A bound versus fraction of competitor to 



total Con A, yield a straight line with virtually identical 



points for both Con A and ADGG-Con A. This result further 



establishes that ADGG-Con A binds to cells by virtue of the 



Con A portion of the conjugate. 



Specific binding of ADGG-Con A and resultant toxicity 



should be inhibitable by the Con A specific carbohydrate 



ligand, a-methyl-D-mannopyraniside. This was tested by 



— fi 

 exposure of H-7 cells to ADGG-Con A at 1 x 10 M for 15 



