Enzymes, con't.

1. Enzymes, con't.

2. Substrate Activation(catalytic mechanisms) • Strain on substrate • Weakens bonds • Makes more accessible for reaction • Acid/base catalysis • Covalent (nucleophilic/electrophilic) catalysis

3. Enzyme kinetics Study of reaction rates—can tell lots about reaction mechanisms

4. Michaelis-Menton Kinetics(saturation kinetics)

5. Leonor Michaelis and Maud Menton--1913

6. Enzyme Action

7. Simplifying assumptions • No back reaction • k3 is rate limiting • [ES] is constant (steady state assumption)

9. Km and Vmax

10. Km • Measure of binding affinity (roughly) • The lower the Km, the tighter the binding • Vmax • Maximum rate of enzyme • Determined by turnover number (kcat) How best to calculate them?

11. Double-reciprocal plot(Lineweaver-Burk)

12. Problems 7a-d,8a,b

13. Regulation

14. Regulation • Irreversible inhibitors—generally not natural part of cell • Drugs and toxins • Covalent modification • Aspirin • Reversible • Substrate level regulation • Competitive inhibitors • Noncompetitive inhibitors • Allosteric regulation (activators and inhibitors) • Covalent modification (reversible) • Proteolytic cleavage

15. Competitive inhibition

16. Noncompetitive inhibition

17. Regulation Reversible • Substrate level regulation • Competitive inhibitors • Noncompetitive inhibitors • Allosteric regulation (activators and inhibitors) • Covalent modification (reversible) • Proteolytic cleavage

20. Reversible covalent modification Phosphorylation Dephosphorylation

23. Proteolytic cleavage Only extracellular