Mechanism of enzyme action

Mechanism of enzyme action -

An enzyme attracts substrates to its active site, catalyzes the chemical reaction by which products are formed, and then allows the products to dissociate (separate from the enzyme surface). The combination formed by an enzyme and its substrates is called the enzyme–substrate complex.

1. Mechanism of Enzyme Action

2. Enzymes Biocatalyst Protein in nature Active Sites Efficiency Specificity Holoenzymes Regulation Location 3D Model of an Enzyme

3. Mechanism of Enzyme Action An enzyme allows a reaction to proceed rapidly under conditions prevailing in the cell by providing an alternate reaction pathway with a lower free energy of activation. The enzyme does not change the free energies of the reactants or products and, therefore, does not change the equilibrium of the reaction. It does accelerate the rate with which equilibrium is reached. The rate enhancement (ratio of the rates of the catalyzed and uncatalyzed reactions) is given by e ΔΔ G ‡ cat/ RT

4. Catalytic Mechanisms 1. Acid–base catalysis 2. Covalent catalysis 3. Metal ion catalysis 4. Proximity and orientation effects 5. Preferential binding of the transition state complex

5. Acid–Base Catalysis

6. Bovine Pancreatic RNase A Secreted by pancreas into small intestine Hydrolyzes RNA to component nucleotides X-Ray structure of bovine pancreatic RNase A

7. Covalent Catalysis

8. Covalent Catalysis Examples

9. Metal Ion Catalysis Carbonic Anhydrase Mechanism

10. Catalysis Through Proximity and Orientation Effects Intermolecular Reaction Intramolecular Reaction is 24 times faster

11. Orientation of S N 2 reaction Any deviation from this optimal geometry would increase the free energy of the transition state and reduces the rate of the reaction.

12. Catalysis Through Preferential Binding of the Transition State Complex An enzyme may bind the transition state of the reaction it catalyzes with greater affinity than its substrates or products! The more tightly an enzyme binds its reaction’s transition state relative to the substrate, the greater is the rate of the catalyzed reaction relative to that of the uncatalyzed reaction. Where transition state stabilization makes only a minor contribution to rate enhancement the enzyme promotes the reaction by instead stabilizing the so-called near attack conformation, a step along the reaction coordinate in which the reactants are properly oriented and in van der Waals contact but have not yet reached the transition state.

13. Proof! Proline Analogs Proline racemase is inhibited by the planar analogs of proline, pyrrole- 2-carboxylate and Δ-1-pyrroline-2-carboxylate, both of which bind to the enzyme with 160-fold greater affinity than does proline. These compounds are therefore thought to be analogs of the transition state in the proline racemase reaction.

14. References Voet , D.; Voet , J.; Pratt, C.W.; Fundamentals of Biochemistry Life at the Molecular Level , 5 th Edition, Wiley Berg, J.M.; Tymoczko , J.L.; Stryer , L; Biochemistry , 7 th Edition, W.H. Freeman and Company New York Harvey, R.A.; Ferrier, D.R.; Lippincott’s Illustrated Reviews: Biochemistry, 5 th Edition, Wolters Kluwer Nelson, D.L.; Cox, M.; Lehninger Principles of Biochemistry , 7 th Edition, W.H. Freeman

15. Thank You.