156 



5. DETERMINATIOX OF MECHANISMS AND CONSTANTS 



but otherwise they provide the means for obtaining expressions for the 

 most common types of enzyme systems and inhibitions. 



The most important conchision reached from inspection of these equa- 

 tions is that errors may be introduced into the determination of Kg or 

 Ki by the presence of other components such as activators or coenzymes 

 (or in enzyme systems wliere the hydrogen ion is involved in the active 

 complex). Let us take one example to illustrate this. We shall assume that 

 plotting the kinetic data gives curves indicating competitive inhibition as in 

 Fig. 5-2. If an activator is present the following errors may be introduced. 



V. 



Fig. 5-2. Example to denionstrate the possible errors 

 in the calculation of K^ and A', in plots of type A. It 

 is assumed that an activator is present (Eq. 5-19). 



To calculate K^ the slope of the uninliil)ited curve is divided by the \jv^ 

 intercept; this will give the true Kg (or the true ^,„ in the general case) 

 only when the presence of the activator on the enzyme does not alter the 

 binding of substrate, i.e., when /? = 1. 



(5-19) 



