SURVEY OF BIOCHEMISTRY Enzyme Kinetics and Inhibition

1. SURVEY OF BIOCHEMISTRYEnzyme Kinetics and Inhibition

2. k v= A P Rates of Chemical Reactions Enzyme kinetics is the study of rates of reactions catalyzedby enyzmes. • The rxn rate (velocity, v) can be described in several ways: • [1] disappearance of reactant, A • [2] appearance of product, P • These eqn’s relate velocity to concentration of reactants and products.

3. k v= A P Rate Laws Enzyme kinetics is the study of rates of reactions catalyzedby enyzmes. • A rate law is an equation describing the velocity of achemical reaction. • Differential Rate Laws • Integrated Rate Laws

4. Differential Rate Laws • Differential rate laws correspond to order of the reaction. Order of Reaction Rate Law 0 v = k 1 v = k [A] 2 v = k [A]2 or k[B]2 or v = k [A] x [B]

5. Rate of Disappearance of A - d[A] A products = k [A] first order rxn dt d[A] Rearranging… = - k dt [A] Integrated Rate Laws:First Order • Integrated rate laws express the rxn velocity in terms of time.

6. d[A] Rearranging… = - k dt [A] Integrated Rate Laws:First Order [A]t Integrate onboth sidesof eqn: dA = - k dt [A]0 (ln [A]t + constant) - (ln [A]0 + constant) = - kt ln [A]t - ln [A]0 = - kt

7. Integrated Rate Laws:First Order ln [A]t - ln [A]0 = - kt ln [A] = ln [A]0 - kt

8. [A]t [A]t ln [A]0 [A]0 = - kt [A]t = [A]0 e -kt Integrated Rate Law:Other Versions of First Order ln [A]t - ln [A]0 = - kt first order rxn Rearranging: Take exponentof both sides: = e -kt first order rxn

9. 2A products Rate of Disappearance of A - d[A] = k [A]2second order rxn dt d[A] Rearranging… = - k dt [A]2 Integrated Rate Law: Second Order • How does the integrated rate law change if the order of the reaction is second order? Show result on board

10. k1 k2 E + S ES E + P k-1 Michaelis-Menten Equation Many enzymes obey Michaelis-Menten kinetics behavior: Rate limiting step Problem: [ES] is difficult to measure!What can we do?

11. k1 k2 E + S ES E + P k-1 Michaelis-Menten Equation Recall Assume equilibrium is maintained in 1st step Assume “steady state” k1 [E] [S] - k-1 [ES] - k2 [ES] = 0 Formation of ES Depletion of ES See notes on board…

12. Michaelis-Menten Kinetics

13. Lineweaver-Burk Plot

14. Enzyme Inhibition • What is an inhibitor? • Modes of Inhibition • Competitivebinds to same site in E as S • Uncompetitive • Noncompetitive • Mixed bind to different site in E than S Note: Text does not distinguish “non” and “mixed”

15. Competitive Inhibition • Competitive inhibitors bind to the same site on E as S

16. Competitive Inhibition

17. Competitive Inhibition

18. Uncompetitive Inhibition Uncompetitive inhibitors bind directly to the ES complex but not to the free enzyme

19. Uncompetitive Inhibition

20. Mixed Inhibition Mixed inhibitors can bind to E or ES complexS cannot bind if I is already bound!

21. Mixed Inhibition

22. Noncompetitive Inhibition Noncompetitive inhibitors can bind to E or ES complexS can bind even if I is already bound! + I See board for plot

23. Updates and Reminders • Exam #2 in two weeks (June 26) • Chapter 7: Protein Function • Chapter 11: Enzyme Catalysis • Chapter 12: Kinetics & Inhibition • Chapter 8: Carbohydrates • Chapter 14: Introduction to Metabolism • Suggested HW problems online this weekend • Resources: What You Should Know more coming soon