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Enzymes, con't.

Enzymes, con't. Substrate Activation (catalytic mechanisms). Strain on substrate Weakens bonds Makes more accessible for reaction Acid/base catalysis Covalent (nucleophilic/electrophilic) catalysis. Enzyme kinetics. Study of reaction rates—can tell lots about reaction mechanisms.

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Enzymes, con't.

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  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)

  8. Km and Vmax

  9. 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?

  10. Double-reciprocal plot(Lineweaver-Burk)

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

  12. Regulation

  13. 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

  14. Competitive inhibition

  15. Noncompetitive inhibition

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

  17. Reversible covalent modification Phosphorylation Dephosphorylation

  18. Proteolytic cleavage Only extracellular

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