Understanding Enzyme Inhibition: Types and Effects

1. Chapter 20 Enzymes and Vitamins 20.4Enzyme Inhibition

2. Enzyme Inhibitors Inhibitors • are molecules that cause a loss of catalytic activity • prevent substrates from fitting into the active sites E + S ES E + P E + I EI no P

3. Competitive Inhibitor Acompetitive inhibitor • has a structure that is similar to that of the substrate • competes with the substrate for the active site • has its effect reversed by increasing substrate concentration

4. Noncompetitive Inhibitor Anoncompetitive inhibitor • has a structure that is much different than the substrate • distorts the shape of the enzyme, which alters the shape of the active site • prevents the binding of the substrate • cannot have its effectreversed by adding moresubstrate

5. Malonate and Succinate Dehydrogenase Malonate • is a competitive inhibitor of succinate dehydrogenase • has a structure that is similar to succinate • inhibition is reversed by adding succinate

6. Irreversible Inhibition In irreversible inhibition, an inhibitor • bonds with R groups at the active site • destroys enzyme activity

7. Irreversible Enzyme Inhibitors

8. Learning Check Identify each description as an inhibitor that is 1) competitive or 2) noncompetitive. A. increasing substrate reverses inhibition B. binds to enzyme surface but not to the active site C. structure is similar to substrate D. inhibition is not reversed by adding more substrate

9. Solution Identify each description as an inhibitor that is 1) competitive or 2) noncompetitive. 1 A. increasing substrate reverses inhibition 2 B. binds to enzyme surface but not to the active site 1 C. structure is similar to substrate 2 D. inhibition is not reversed by adding more substrate