616 13. REVERSAL OF INHIBITION 



and the conservation equations may be written as: 



(E,) = (E) + (EI) + (ES) (13-17) 



(I^) = (I) + (EI) + (RI) (13-18) 



(R,) = (R) + (RI) (13-19) 



For systems m which mutual depletion does not occur (zone A), the term 

 (EI) may be omitted from Eq. 13-18. It will be convenient to treat non- 

 competitive inhilntion since other types of inhibition are generally only 

 extensions of this and the corresponding equations may be easily obtained. 

 The substrate reaction can be neglected for noncompetitive inhibition smce 

 the presence of substrate will not modify the inhibition. We are now left 

 with two possibilites: either (R,) is much greater than (I^) so that the 

 concentration of the reversor is not appreciably reduced by reaction with 

 the inhibitor, in which case (R,) = (R), or (R,) and (I,) are comparable 

 and the reaction reduces the concentrations of both. 



In the first case, where (R,) = (R), it can be easily shown that: 



/C(E,) ^ _^ra.)__ (13.20) 



^^^ = (I)+Z, ^^ (R.) + ^r 



Combining these two equations and substituting in ; =- 1 — [(E)/(Ei): 



^^''^ (13-21) 



(I/) + 1 + (R/) 



Thus the presence of a reversor lowers the inhibition to the same degree 

 as the substrate in competitive inhibition, if the specific concentrations of 

 the reversor and substrate are equivalent. The addition of a reversor to 

 a competitive system would lower the inhibition to: 



: ^lil (13-22) 



(I/) -f 1 + (S') + (R/) 



The dependency of the inhilntion on the concentration of the reversor for 

 different values of K, is shown in Fig. 13-5. From such families of curves 

 it is possible to visualize the effectiveness of a particular reversor. To 

 use a reversor properly, so that the results can be accurately interpreted, 

 it is necessary to know at least approximately the dissociation constants, 

 K, and A%. The use of a reversor with a K, much higher than Ki would not 

 be expected to diminish the iidiilution unless its concentration were a good 



