578 



12. RATES OF INHIBITION 



expressed in equations applicable to the steady state. The situation can be 

 represented by the following reactions: 



^ I, + E ^ EI 



1 j^2 ^-1 



(12-85) 



The spatial relationship between the susceptible enzyme and the enzyme 

 inactivating the inhibitor can be an important factor in determining how 

 effectively the inhibitor concentration at the susceptible enzyme is reduced. 

 A rigorous kintic treatment is quite difficult but the behavior of the system 

 will follow the curves in Fig. 12-23. 



TIME ^ 



Fig. 12-23. Effect of metabolic inactivation 

 of the inhibitor on the rate of inhibition 

 (scheme 12-85). Curve A, no inactivation 

 occurs. Curve B, inactivation progressively 

 reduces the inhibitor concentration — inhi- 

 bition irreversible. Curve C, same as B but 

 supply of inhibitor is limited and the inhi- 

 bition is reversible. Curve D, inactivation 

 prevents the inhibitor from reaching the 

 same initial concentration (as when the 

 inactivating system is effective before the 

 inhibitor attacks the enzyme). 



(F) Adaptatio7i of the cell to the inhibition. Adaptation of metabolism to 

 the action of an inhibitor is usually too slow to affect the rate kinetics of 

 the inhibition, but occasionally adaptation is very rapid and shifts in meta- 



