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SURVEY OF BIOCHEMISTRY Enzyme Catalysis 1 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‡ 2 Catalytic Mechanisms: Learning Goals • Types of Catalysis – Acid-Base Catalysis – Covalent Catalysis – Metal Ion Catalysis • Examples – Lysozyme – Serine Proteases 3 PRS • What is a Lewis base? 1. A molecule that 2. A molecule that 3. A molecule that pair 4. A molecule that pair donates H+ donates OHdonates an electron accepts an electron 4 PRS • Which of the following is a Schiff base (imine) group? 1. 3. 2. 4. Table 1-2 5 Acid-Base Catalysis • General acid catalysis H+ transfer from an acid lowers the free energy of the transition state 6 Base Catalysis • General base catalysis H+ is abstracted by a base to lower the free energy of the transition state 7 Example: RNase A • Function: Truncate RNA • Observations – Isolated RNA intermediates – Ionizable residues detected – Chemical derivatization – Structure determination by x-ray crystallography 8 Example: RNase A 9 Example: RNase A 10 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 11 Nucleophiles & Electrophiles Electron pair donor or negative charge Electron-deficient atoms 12 Metal Ions as Catalysts CO2 + H2O HCO3- + H+ Example: Carbonic Anhydrase 13 Lysozyme Lysozyme cleaves polysaccharides via a covalent reaction mechanism 14 Serine Proteases Serine proteases involve covalent catalysis, general base catalysis and electrostatic interactions 15