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Example CD7-4
Derive a Rate Law For Non-Competitive Inhibition

 
    Solve for the concentrations of the complexes (IE) and (IES) in terms of the free enzyme concentration, (E), and substrate concentration, (S), in a manner similar to that for (ES); substitute these expressions in the total enzyme balance and then obtain the rate law for noncompetitive inhibition. (Let Ks, KI,,and represent the equilibrium constants for reactions 1 through 4, respectively.)  
       
    Solution  
    For reaction 2,  
     
   

(EI) =KI (I)(E)

(CDE7-4.1)
    We can use either Equation (CD7-19),  
     
   

IMAGE 07eq38.gif

(CDE7-4.2)
    or (CD7-20),  
     
   

IMAGE 07eq39.gif

(CDE7-4.3)
     
    to express IES in terms of ImiddotE, and S.
The mole balance on the total amount of enzyme, bound and free (E), is
   

Et = E + ES + IE + IES

(CDE7-4.4)
       
    Substituting Equations (CD7-24), (CDE7-4.1), and (CDE7-4.2) into (CDE7-4.4) and rearranging gives us  
     
   

IMAGE 07eq40.gif

(CDE7-4.5)
       
    The rate of formation of the product for a noncompetitive inhibition of an enzymatic reaction is  
     
   

IMAGE 07eq41.gif

(CDE7-4.6)