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THE BIOCHEMISTRY OF B VITAMINS 



By plotting the reciprocal of the rate, 1/r, against the reciprocal of the 

 concentration of the substrate, 1/[S], a linear relationship should result 

 at a constant concentration of inhibitor. The characteristics of slope and 

 extrapolated intercept at 1/[S]=0 are as follows for various types of 

 inhibitions. 



1/[S] 



Figure 1. Relationship of reciprocal of the rate of an enzymatic reaction to the 

 reciprocal of substrate concentration as a method of determining type of inhibition. 



Competitive Inhibition 



Noncompetitive Inhibition 



_._._._. "Uncompetitive" Inhibition 

 -x-x-x-x In absence of Inhibitor 



For the uninhibited enzyme reaction, the extrapolated intercept should 

 represent 1/R, where R is the maximum rate of the enzymatic reaction 

 at enzyme saturation, and the slope should be K s /R. The ratio of slope 

 to intercept is the dissociation constant of the enzyme-substrate complex. 



For competitive inhibition, the intercept for various concentrations of 

 the inhibitor is constant, 1/R. However, the slope of the linear relation- 

 ship is Ks/R + Ksm/KjR, and is dependent upon the concentration of 

 the inhibitor. 



For noncompetitive inhibition, both the slope and intercepts are 

 changed. The usual case is such that the combination of the inhibitor 

 with either enzyme or enzyme-substrate complex occurs with approxi- 

 mately equal affinity, so that Ki and K S i are approximately equal. Under 



