PRODUCT INHIBITION 



143 



at the beginning, there is no reaction until the substrate concentration 

 reaches a critical value and above this the rate increases as in Fig. 4-17. 

 The differences between curves I and II represent the effect of the reverse 

 reaction superimposed on the inhibition due to the binding of the product 

 on the active center. 



Inhibition by Combination of the Product in an Inactive Complex 



The product can inhibit the forward reaction competitively, noncompe- 

 titively, or in any other way discussed in general inhibition. The general 



3mM 



CP)- 



FiG. 4-18. Noncompetitive product inhibition by tlie forma- 

 tion of an inactive complex between the product and tlie 

 enzyme. In the upper graph A the rate is plotted against the 

 product concentration and in the lower graph B the frac- 

 tional inhibition is plotted against the product concentra- 

 tion. Curves I: A% = 0.1 mlf; curves II: Kj, = 0.3 raM; 

 curves III: Kj, = \ mM; curves IV: A'j, = 10 mil/; curves V: 

 K = 50 Yi\M; curves VI: no inhibition. 



