COMBINATION WITH MOLECULES OF INHIBITORS 



93 



Finally, if « has a value near unity, an intermediate situation occurs in 

 which both inhibitor molecules play a role in the inhibition. Comparison of 

 curve 4 with curve 1 in Fig. 3-19 shows that when a = 1, the inhibition 

 will be appreciably greater than for the case where n = I. 



When /5 = 1 there is no effect on the enzyme reaction produced by the 

 binding of the first inhibitor molecule and in this case: 



ar 



a + «(!') + ar 



= 1 



(3-88) 



Fig. 3-19. Plots of Eq. 3-84 for different values of the constants a and /3. Curve 1: 



n^\; curve i: a = 0.1, ^ = 1; curve 3: « = 0.01, ^3 = 1; curve 4: « = 1; /3 = 0; 



curve 5: a = I, B = 1; curve 6: a = 10; (3 = 1. 



When a is very low the inhibition becomes high whereas when a is high the 

 inhibition is reduced: in the former case the inhibition is governed by the 

 binding of the second inhibitor molecule and tends to follow an equation 

 of the type: 



(I) 



(I) + ccK, 



1, 



low 



(3-89) 



and in the latter case the binding of the second inhibitor molecule is so 

 weak that little inhibition occurs. When a is around unity, the inhibition 

 is generally less than when n = 1 because only the binding of the second 

 inhibitor molecule is inhibitory and it occurs to a lesser extent than the first 

 molecule [the ratio of (EI)/(E/) is more than (El2)/(E^) when a = 1]. 

 This may be seen by comparing curve 5 with curve 1 in Fig. 3-19. The other 

 curves given show the effect of a on the degree of inhibition. 



