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 k 3 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 (k cat ) How best to calculate them?

11. Double-reciprocal plot (Lineweaver-Burk)

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

13. Regulation

14. 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