Enzyme Inhibition (26.4)

1. Enzyme Inhibition (26.4) • Inhibition is a term used to describe the inability of a product being formed due to the presence of another substance (the inhibitor) • Enzyme inhibition can be competitive or noncompetitive • Competitive inhibition is caused when an inhibitor “competes” with the substrate in binding with the enzyme • Inhibitor decreases production of ES, thus decreasing product formation • Noncompetitive inhibition is caused when an inhibitor can bind to either the free enzyme or the enzyme-substrate complex • Inhibitor does not allow ES complex to convert to products

2. Enzyme Inhibition – Competitive (26.4) • Competitive inhibition does not affect the maximum rate of the catalytic process, but does slow down the process • Competitive inhibition can be eliminated by increasing the substrate concentration • Preequilibrium approximation is used to eliminate [ES] and [EI] • Lineweaver-Burk plots can be used to distinguish inhibition • For competitive inhibition, the maximum rate is unchanged (y-intercept is not dependent on [I]) • The effective Michaelis constant (Km*) is dependent on inhibitor concentration • For different concentrations of inhibitor, LB plots give lines with different slopes

3. Enzyme Inhibition – Noncompetitive (26.4) • Noncompetitive inhibition does affect the maximum rate of the catalytic process, but does not affect the binding of substrate to the enzyme • Noncompetitive inhibition cannot be eliminated by adding more substrate (Rmax depends on inhibitor concentration) • Preequilibrium approximation is used to eliminate [ES], [EI], and [ESI] • Lineweaver-Burk plots can be used to distinguish noncompetitive inhibition from competitive • For noncompetitive inhibition, the maximum rate is changed (y-intercept is dependent on [I]) • The Michaelis constant is the same as that of the uninhibited case (slope of line is not the same however, why?)

4. Enzyme Inhibition

5. Competitive Inhibition

6. Noncompetitive Inhibition