RATES OF IXHIEITION OF PURE ENZYMES 



541 



varies exponentially. The time required to produce 50% inhil)ition is 

 given bv: 



to. 



2.3 



0.5 



if 



(12-(3) 



whereas the time required to produce an inliibition half that of the final 

 iidiibition would be given by: 



^0.5, = 0.69/a 



(12-7) 



10 - 



Fig. 12-4. Hypothetical inhibition curves for two inhibi- 

 tors to ilhistrate the problems involved in comparing 

 rates of inhibition. 



In the former case. ^0.5 depends on the final inhibition i^ but in the latter 

 case it does not and hence Eq. 12-7 is a valid expression of the inhibition 

 rate whatever the eventual inhibition or the concentration of the inhibitor. 

 It is therefore suggested that it would be generally preferable to give the 

 values of ^0.5, rather than ^q.s- 



RATES OF INHIBITION OF PURE ENZYMES 



The kinetic treatment of inhibition rates will vary with the type of 

 inhibition. It will be convenient to start with the simplest situation in 

 which a single inhibitor molecule combines with each enzyme molecule to 

 inhibit noncompetitively. This reaction may be represented as: 



E + I;^EI 



(12-8) 



