10968

Enzyme Inhibition Kinetics

This Demonstration plots rate data for Michaelis–Menten enzyme kinetics for four types of inhibition. For competitive inhibition, an inhibitor forms an inactive complex with the enzyme. For uncompetitive inhibition, an inhibitor forms an inactive complex with the enzyme-substrate complex. For mixed inhibition, the inhibitor forms both types of inactive complexes. For self-inhibition, the substrate itself inhibits the reaction by forming an inactive complex with the enzyme-substrate complex.
Select "Michaelis–Menten" to plot the rate of substrate consumption versus substrate concentration. Select "Lineweaver–Burk" to plot versus so as to obtain a straight line (except for the self-inhibited case). The slope and intercept of this line are related to , , and . Use the slider to change the inhibitor concentration, which changes the slope and/or the intercept, depending on which type of inhibition is selected. When self-inhibited is selected, the substrate concentration is the inhibitor concentration, so the slider is hidden.

SNAPSHOTS

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DETAILS

Reaction Pathways
values come from respective reaction coefficients
represents the concentration of an enzyme-substrate complex
represents the concentration of an enzyme-inhibitor complex
represents the concentration of an enzyme-inhibitor-substrate complex
is the total enzyme concentration
,
,
.
The Linweaver–Burk method in a method of linearizing experimental data. The slope and intercept from experimental data can be used to determine , , and from plotted data.
The line is given by
,
where is the slope, is the intercept, and is the intercept (the value of when ).
Competitive Inhibition: The inhibitor competes with the substrate for the enzyme to form an inactive complex.
(1)
(2)
(3)
(4) (inactive)
(5)
,
,
,
,
.
Uncompetitive (Anti-Competitive) Inhibition: The inhibitor binds to the enzyme-substrate complex forming an inhibitor-enzyme-substrate complex.
(1)
(2)
(3)
(4) (inactive)
(5)
,
,
,
,
.
Noncompetitive Inhibition (Mixed Inhibition): Mixed inhibition is most commonly seen for enzymes with two or more substrates. The inhibitor can bind to the enzyme or enzyme-substrate complex. The substrate can also bind to the inhibitor-enzyme complex.
(1)
(2) (inactive)
(3)
(4) (inactive)
(5) (inactive)
,
,
,
,
.
Substrate Inhibition: In the case of uncompetitive inhibition, the inhibitor ties up the enzyme-substrate complex to form an inactive substrate-enzyme-substrate complex.
(1)
(2)
(3)
(4) (inactive)
(5)
,
;
this plot in not linear because the intercept depends on the substrate concentration .
Reference
[1] H. S. Fogler, Essentials of Chemical Reaction Engineering, 1st ed., Upper Saddle River, NJ: Pearson Higher Education, 2010 pp. 364–370.
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