INTERACTION WITH CHOLINESTERASE 



289 



Table 6-24 



Interaction Energies or Substituent Halogen Groups with Plasma and 



Erythrocyte Cholinesterase " 



" The subscripts refer to the compounds compared and specifically to the substi- 

 tuted group on the acetate radical; both butyl- and isoamylesters were averaged 

 from the data of Adams and Whittaker (1950). The calculated differences in free 

 energy between the groups for the plasma enzyme were obtained from Table 6-19. 

 The calculations for the erythrocyte enzyme assume maximal ion-dipole interaction: 

 Eq. 6-57 was used with the following values — /<c-cl = -••^' /'C-Br = 2.2, d^ — 4.43 A 

 for C-Cl and 4.52 A for C-Br. and D = 14.3. The dipole moment of the C-CH3 

 bond was considered negligible for this interaction. The configuration assumed was: 



^ 



C+ - C+ 



/ 



on the basis of their polarizabilities; the ion-dipole energies for the C— CI 

 and C— Br dipoles would be roughly the same inasmuch as the dipole mo- 

 ments are similar. Furthermore, if these substances are bound like the 

 acetylcholine molecule, the anionic site would be expected to be at some 

 distance removed from these substituted groups. If they are not bound in 

 this manner, the anionic site could interact with both the 



- -f/ 

 0=C 



\ 



group and the terminal dipole, increasing the stability of the complexes, 

 the chlorine derivative being somewhat more stable than the bromine 

 derivative due to its slightly higher dipole moment. In this position, the 

 substituent groups might not interact with the protein and the dispersion 

 contribution from them might be neglected. The calculation for the ion- 



