280 



6. INTERACTIONS OF INHIBITORS WITH ENZYMES 



separation of 3.70 A or a group center separation of approximately 4.30 A. 

 Van der Waals' radii give minimal separation of 3.85 A and maximal se- 

 paration of 4.56 A, depending on the orientation of the groups, so that 



Fig. 6-17. Plot of Eq. 6-90 for ion-ion interactions, assuming that 



jU = 0.16, for the purpose of estimating equihbrium distances from 



experimental interaction energies. 



the calculated value is in very satisfactory agreement assuming direct 

 group contact. These results are very similar to those calculated by Nis- 

 onoff and Pressman (1957). 



Specificity of the Ionic Group 



Antibody to the p-azophenylarsonate group will react equally with the 

 corresponding phosphonate group, but will not react with sulfonate, car- 

 boxylate, methylarsonate, or stibonate groups (Pressman et al., 1945). 

 Antibodies to the benzoate group will similarly not combine with the cor- 

 responding sulfonate or arsonate (Nisonoff and Pressman, 1957). In the 

 former case the specificity is surprising inasmuch as the sulfonate and 

 carboxylate groups are smaller than the arsonate group and would be 

 expected to fit in satisfactorily. The difference in binding energy between 



