618 13. REVERSAL OF INHIBITION 



The following ratios may then be calculated: 



On the other hand, if the inhibition in each case is to be reduced to a cer- 

 tain designated value, if, the ratio is given by: 



(R.) 





1 



(13-25) 



The ratio now does not vary so widely with the initial inhibition but 

 changes in the opposite direction compared to the former situation. 



Thus the ratio, (R;)/(I^), is not proportional to K^jKi, as has occasionally 

 been assumed, and is equal to it only when the initial inhibition is high and 

 is reduced 50% by the reversor. 



The more general case, where (R,) = (R) -1- (RI) and mutual depletion 

 of reversor and inhibitor occurs, may now be treated. The simplest approach 

 is to calculate the free inhibitor concentration in the presence of the reversor 

 and use this concentration to determine the inhibition. The quadratic equa- 

 tion for the free inhibitor concentration is: 



(I)^' + [(Re) - (1,) + Kr]{\) - KAh) = 



(13-26) 



Plots of the inhibitions obtained by such a procedure are sliown in Fig. 

 13-6 for a system with the same inhibition characteristics as in Fig. 13-5. 

 As the affinity of the reversor for the inhibitor increases, the symmetrical 

 sigmoid curves become distorted. There is not so much difference in the 

 effects produced at lower concentrations of the reversor but very marked 



