1. Enzyme Regulation

2. Enzyme Regulation Inhibition Allosteric Regulation Competitive
Noncompetitive
Allosteric Regulation
Activation

3. Inhibitors A molecule that binds to an enzyme
preventing it from catalyzing reactions.
If binding involves covalent bonds, then
inhibition is often irreversible.
If binding is weak, inhibition may be reversible.
Reversible inhibition of enzymes is a natural
part of the regulation of metabolism.

4. Competitive Inhibition
Inhibitor binds to the same site as the substrate
Think: How do you overcome a competitive inhibitor?
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig a,b

5. Effect of competitive inhibitor on saturation curve

6. Application of competitive inhibition: overcoming alcoholism

7. Noncompetitive Inhibition
Inhibitor binds somewhere other than the
active site
Causes enzyme to become insensitive to
substrate concentrations
Brainstorm ways in which an inhibitor could decrease substrate binding without binding to the active site.

8. Mechanism of Noncompetitive Inhibition
Alters enzyme conformation rendering the
active site unreceptive or less effective

9. Effect of noncompetitive inhibitor on saturation curve

10. Thought Questions Can you overcome noncompetitive inhibition
by adding more substrate? Explain.
Why do inhibitors naturally exist? What necessary role do they play in the human body?

11. Why do inhibitors exist?

12. Negative feedback or feedback inhibition

14. Why do inhibitors exist?
Maintaining homeostasis

15. Video: Enzyme Inhibition
Tutorial Animation
/animations/enzyme_inhibition/e nzyme_inhibition.htm

16. Allosteric Site a specific binding site on the enzyme that is
not the active site
can be located between subunits (where
subunits join)

17. Allosteric Enzyme Usually large,quaternary structure
has a second binding site that is not the
active site (allosteric site)
has two conformations: active and inactive
naturally oscillates between the two
conformations
binding of the molecule (effector) to the allosteric site can stabilize one of the conformations

18. Effectors: Allosteric Regulators
a regulator that can activate or inhibit by the
enzyme by binding to an allosteric site
changes enzymatic activity by binding
weakly to an allosteric site
Classifications:
Allosteric inhibitor: stabilizes the conformation
that lacks an active site (inactive form)
Allosteric activator: stabilizes the conformation that has a functional active site

19. Allosteric Regulation
Regulating an enzyme’s activity with an allosteric regulator (effector) that binds to the allosteric site
Type of effector results in one of two
allosteric regulation mechanisms:
Allosteric Inhibition
Allosteric Activation
Notice that for our purposes, this is the same as noncompetitive inhibition

20. Notice that for our purposes, this is the same as noncompetitive inhibition

21. Allosteric Regulation & Cooperativity
If the allosteric site is located between subunits, then the binding of one effector could stabilize the conformation of all the other subunits
This is known as cooperativity
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 6.18b

22. Cooperativity
Binding of a molecule (substrate or effector) stabilizes a conformational change on all the other subunits
Can only occur in enzymes with multiple
subunits (quaternary structure) and multiple active sites
Can result in an increase or decrease in
substrate affinity

23. Cooperativity Positive cooperativity: Negative cooperativity:
Substrate binding
Effector (activator)
binding
Negative cooperativity:
Effector (inhibitor) binding
Example: some forms of
noncompetitive inhibition
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 6.20

24. Activity: Consolidate Terms
Use a graphic organizer to show the relationship between these terms listed on the right
Graphic organizers that may be useful in this activity are:
Mind map
Flow charts
Venn diagram
Terms
Inhibition
Competitive inhibition
Noncompetitive inhibition
Allosteric regulation
Allosteric inhibition
Allosteric activation
Allosteric inhibitor
Allosteric activator
Cooperativity
Positive cooperativity
Negative cooperativity
Substrate
Active site
Allosteric site

25. HW Question Compare allosteric activation and positive cooperativity.
Compare noncompetitive inhibition and negative cooperativity.
Remember: “Compare” means you’re looking at both similarities and differences. And the similarities should indicate the relationship between the 2 items and the reasons why they are being compared in the first place.