240 



6. INTERACTIONS OF INHIBITORS WITH ENZYMES 



the relative values of a and h (Eq. 6-50) and the potential energy cp^. An 

 empirical approximation of this difference is: 



d,=d, + (0.5/V Ve - l) 



(6-72) 



based on the relative velocities of oscillatory movement at different points 

 on the path d-^d^^,. In general, d^ — d^ will be between 0.2-0.4 A for most 

 interactions of interest in enzymology. 



Table 6-13 

 Bond Axgles 



0- 



R. 



118^ Nl 

 1110 \ ^' i- 



T CH 

 jiooV^ ynQo 



Amino acids 



1180 



240 



0- 



Another approach to this problem is to assume that a molecule creates 

 a cavity, due to the internal pressure arising from its thermal motion, the 

 radius of this cavity being greater than the molecular radius. Equating 

 this outward pressure with the electrical pressure, which is related to the 

 energy of charging of an ion in the cavity and is directed inward, the cav- 

 ity radii for ions in water have been estimated (Benson et al., 1957). 

 Figure 6-10 presents the relation betv.'een ion size and cavity size; for most 



