108 



I. M. KLOTZ 



13 



Fig. 16. Molecular models of 



Top: 



(CH3)2N 



-// 



— N=N- 



\_ 



/ 







c 



o- 



Bottom: 



(CH3)2N— (^ \— N=N— / S— CH=CH— C 



/- 



O 



o- 



right), has a base structure which is fundamentally identical with the upper 

 one but in which we replace the anionic group by a cationic group. Despite 

 the fact that the protein carries a negative charge, and the organic molecule is 

 plus charged, there is essentially no binding. There are a few points in the lower 

 curve slightly above the zero axis, but when you get to these higher concentra- 

 tions we can not even be positive that these points are significant, because we 

 are measuring small differences between very large numbers. 



Why should this be true? Presumably there is some specificity in the protein 

 configuration. We have an explanation, which initially we thought of in a dif- 

 ferent connection, which would account for the difference in anionic vs. cationic 

 binding automatically. I am not absolutely sure it is true, but certainly it seems 

 to me at the present time to be convincing, and so I thought I might outline it 

 in the next illustration (Fig. 19). 



We indicate, first, again going backward a little, where I think the origin of 



