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13. REVERSAL OF INHIBITION 



competitive or noncompetitive, and on whether we are dealing with mutual 

 depletion systems or not. A dilution factor, r, is defined by the equation 

 r = (Io)/(Iy) and thus is the ratio of initial to final inhibitor concentrations. 

 Initial and final inhibitions may then be written as: 



Noncompetitive: 



(I') 



(D + 1 



d') 



d') 



(13-10) 



Competitive: 



(D 



(D + 1 + (S') 



(!') 



(D + r + (S') 



(13-11) 



The effects of varying degrees of dilution on the final inhibition are shown 

 for some specific cases in Fig. 13-2. It is particularly interesting to com- 



1000 



Fig. 13-2. Effects of varying degrees of dilution on the final inhibition (Eqs. 13-10 

 and 13-11). The dilution factor, r, is equal to the ratio of the initial and final inhibitor 

 concentrations, (Io)/(I/). Noncompetitive: curve A, K^ = 1 mil/, (I) = 5 mM; curve B, 

 Ki = 0.1 mM, (I) = 5 mM. Competitive: Curve C, Ki = 0.1 mM, K, = I mM, (I) ^ 

 0.5 mM, and (S) = 1 mM; curve D, K^ = 0.05 mM, K, = 1 milf , (I) = 0.5 mM, 



and (S) = 1 mM. 



pare curves A and D where the initial inhibition is the same; dilution is 

 seen to be more effective in reducing the inhibition in noncompetitive sys- 

 tems than in competitive ones. The reason is that in the competitive 

 case the substrate concentration is also reduced by dilution and the sub- 

 strate is increasingly less effective in antagonizing the inhibition. It is 

 also worth noting that the larger K^, the more readily will dilution reduce 

 the inhibition, comparing curves A and B. This means that when one starts 

 out with a relatively high inhibition in a noncompetitive system, it requires 



