Chemistry 2100

1. Chemistry 2100 Lecture 11

2. Protein Functions Binding + L PL P Catalysis Structure

3. Why Enzymes? • Higher reaction rates • Greater reaction specificity • Milder reaction conditions • Capacity for regulation • Metabolites have many potential pathways of decomposition • Enzymes make the desired one most favorable

4. Specificity: Lock-and-Key Model • Proteins typically have high specificity: only certain substrates bind • High specificity can be explained by the complementary of the binding site and the ligand. • Complementarity in • size, • shape, • charge, • or hydrophobic / hydrophilic character • “Lock and Key” model by Emil Fisher (1894) assumes that complementary surfaces are preformed. +

5. Specificity: Induced Fit • Conformational changes may occur upon ligand binding (Daniel Koshland in 1958). • This adaptation is called the inducedfit. • Induced fit allows for tighter binding of the ligand • Induced fit can increase the affinity of the protein for a second ligand • Both the ligand and the protein can change their conformations +

8. Apoenzyme + Coenzyme = Holoenzyme

9. Apoenzyme + Coenzyme = Holoenzyme

10. Apoenzyme + Coenzyme = Holoenzyme

11. Apoenzyme + Coenzyme = Holoenzyme

12. Enzymatic Activity • increase [reactant] • increase temperature • add catalyst Potential Energy Reactants Products Reaction

13. TS • increase [reactant] • increase temperature • add catalyst Potential Energy Reactants Products Reaction

14. TS Ea • increase [reactant] • increase temperature • add catalyst Potential Energy Reactants Products Reaction

15. TS Ea • increase [reactant] • increase temperature • add catalyst Potential Energy Reactants Products Reaction

16. TS Ea • increase [reactant] • increase temperature • add catalyst Potential Energy Reactants Products Reaction

17. TS Ea • increase [reactant] • increase temperature • add catalyst Potential Energy Reactants Products Reaction

18. Ea ' TS Ea • increase [reactant] • increase temperature • add catalyst Potential Energy Reactants Products Reaction

19. How to Lower G? Enzymes organizes reactive groups into proximity

20. How to Lower G? Enzymes bind transition states best

21. H2O + CO2HOCO2– + H+ Potential Energy Reaction

22. H2O + CO2HOCO2– + H+ Potential Energy Reaction

23. H2O + CO2HOCO2– + H+ Potential Energy Reaction

24. H2O + CO2HOCO2– + H+ Potential Energy Reaction

25. H2O + CO2HOCO2– + H+ Potential Energy Reaction

26. H2O + CO2HOCO2– + H+ Ea Potential Energy Reaction

27. Ea ' H2O + CO2HOCO2– + H+ Ea Potential Energy Reaction

36. How to Do Kinetic Measurements

37. Enzyme Activity Figure 23.3 The effect of enzyme concentration on the rate of an enzyme-catalyzed reaction. Substrate concentration, temperature, and pH are constant.

38. Enzyme Activity Figure 23.4 The effect of substrate concentration on the rate of an enzyme-catalyzed reaction. Enzyme concentration, temperature, and pH are constant.

39. Enzyme Activity Figure 23.5 The effect of temperature on the rate of an enzyme-catalyzed reaction. Substrate and enzyme concentrations and pH are constant.

40. Enzyme Activity Figure 23.6 The effect of pH on the rate of an enzyme-catalyzed reaction. Substrate and enzyme concentrations and temperature are constant.

43. What equation models this behavior? Michaelis-Menten Equation