REVERSAL IN CELLS AND WHOLE ANIMALS 



641 



destruction of the inhibitor. If we assume that the dissociation of Ejl is 

 rapid compared to the destruction of the inhibitor, the inhibition may be 

 calculated from the value of (I) at any time. Since the rate of reaction 13-65 

 is given by the usual Michaelis-Menten expression: 



dd) A-4(E,)(I) 



dt (I) + K,., 



(13-67) 



2 4 



TIME (HRS.)- 



10 12 14 16 



18 20 



Fig. 13-14. Time courses of inhibition of .serum eholine.sterase by 

 physostigmine (Eq. 1.3-64). Curve B fits the exiaeriniental data obtained 

 by ElHs et al. (1943) while curves A and C are plotted for the same 

 inhibition constants but different initial concentrations of physo- 

 stigmine. In all case k2(F,f)/Kj = 1.4. 



the variation of (I) with time may be obtained by integration of this equa- 

 tion with the assumption that / = i^ at ^ = 0: 



K, 



1 



'"T 



+ K, 



1 



1 



= k,iE,)t (13-68) 



This is similar to Eq. 13-63 but there is a greater possibility of variation in 

 the forms of the reversal curves, arising from different relative values of 

 K^ and K,,^. 



