1 SURVEY OF BIOCHEMISTRY Enzyme Catalysis

2 Enzymatic Catalysis: Recap General Properties of Enzymes –6 Enzyme Classes –Substrate Specificity –Types of Cofactors Transition State Diagrams –Activation Energy –Reactions vs. Products –∆G vs ∆G ‡

3 Catalytic Mechanisms: Learning Goals Types of Catalysis –Acid-Base Catalysis –Covalent Catalysis –Metal Ion Catalysis Examples –Lysozyme –Serine Proteases

4 PRS What is a Lewis base? 1.A molecule that donates H + 2.A molecule that donates OH - 3.A molecule that donates an electron pair 4.A molecule that accepts an electron pair

5 PRS Which of the following is a Schiff base (imine) group? Table 1-2

6 Acid-Base Catalysis General acid catalysis H + transfer from an acid lowers the free energy of the transition state

7 Base Catalysis General base catalysis H + is abstracted by a base to lower the free energy of the transition state

8 Example: RNase A Function: Truncate RNA Observations –Isolated RNA intermediates –Ionizable residues detected –Chemical derivatization –Structure determination by x-ray crystallography

9 Example: RNase A

10 Example: RNase A

11 Covalent Catalysis Covalent catalysts accelerate rxns by forming a covalent bond between E and S. Explain conversion of acetoacetate to acetone on board Figure 11-11

12 Nucleophiles & Electrophiles Electron pair donor or negative charge Electron-deficient atoms

13 Metal Ions as Catalysts Example: Carbonic Anhydrase CO 2 + H 2 OHCO H +

14 Lysozyme Lysozyme cleaves polysaccharides via a covalent reaction mechanism

15 Serine Proteases Serine proteases involve covalent catalysis, general base catalysis and electrostatic interactions