REVERSAL BY DESTRUCTION OF INHIBITOR 



637 



REVERSAL OF INHIBITION BY DESTRUCTION OF 

 INHIBITOR 



Decline in the enzyme or metabolic inhibition as the result of the des- 

 truction of the inhibitor sometimes occurs in pure enzyme preparations but 

 is more common in homogenates or cellular preparations. Destruction of the 

 inhibitor may be enzymic or nonenzymic; if it is enzymic, the reaction may 

 be catalyzed either by the inhibited enzyme or by another enzyme occur- 

 ring in the mixture. The total time course of inhibition in such cases will 

 follow curves of the type shown in Fig. 13-12. Curves A, B, and C represent 



TIME 



Fig. 13-12. Time courses of inhibition assuming 

 destruction of the inhibitor. Curves A, B, and C 

 show three different concentrations of the inhibitor 

 for a situation in which the rate of inhibition is 

 rapid; the different forms of the curves may be 

 noted. In curve D the rate of inhibition is slower 

 so that equilibrium inhibition is never reached. 



situations in which the inhibitor reacts rapidly with the enzyme whose in- 

 hibition is being measured and then is more slowly destroyed, so that the 

 maximal inhibitions reached approximate the equilibrium inhibition ex- 

 pected. These three curves are plotted for different initial concentrations 

 of the inhibitor. Curve D illustrates a situation in which the rate of inhibi- 

 tion and the rate of destruction of the inhibitor are more comparable and 

 here an equilibrium inhibition is never reached due to the appreciable loss 

 of the inhibitor while the inhibition is developing. When this occurs, inhi- 



