PSEUDO-IRREVERSIBLE INHIBITION 



79 



If the inhibitor is specific for a certain enzyme, being bound to nothing 

 else, it may be said to titrate the enzyme, in the sense that the amount of 

 enzyme inactivated will be equivalent to the amount of inhibitor added. The 

 rates of reaction are determined at different enzyme concentrations, with 



Fig. 3-14. Plot of rate against the enzyme 



concentration for pseudo- irreversible and 



irreversible inhibition. 



and without inhibitor, and these rates are plotted against (E^) in arbitrary 

 units since the molar concentration of enzyme is generally not kno\vm. In 

 the absence of inhibitor, one obtains a straight line passing through the 

 origin, since v = A"(E,); in the presence of inhibitor a straight line of identical 



I - 



CEJ- 



Fig. 3-15. Variation of the fractional 

 inhibition with the enzyme concentration 

 for pseudo-irreversible inhibition where 



i = (I,)/(E,). 



slope is obtained but intercepting the (E^) axis at a point where (E,) = (I,). 

 Irreversible inhibitors will also yield the same results. Such a plot is shown 

 in Fig. 3-14 and the hyperbolic curve when inhibition is plotted against 

 (E,) is illustrated in Fig. 3-15. 



