Chapter 6_1

Chapter 6_1 - III. Catalytic Mechanisms: factors...

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III. Catalytic Mechanisms: factors contributing to enzymes’ catalytic activity. Note: enzymes may use one or more of these general strategies. a. Proximity and orientation 1. When an enzyme binds a substrate, it brings the enzyme and substrate together and also orients susceptible bonds, so the enzyme and substrate are close together and therefore can react b. Preferential transition state binding 1. This idea is a black eye to the old lock and key idea 2. If the enzyme were complementary to the substrate, it would never get to the transition state because the substrate would never be able to get to the transition state. The enzyme would literally hold the substrate in its initial form. 3. The enzyme’s binding site/pocket (not the substrate) preferentially stabilizes the transition state The product cannot go back to the substrate form with the same enzyme a. If you make a molecule that looks like the transition state it binds to the molecule c. General acid-base chemistry 1. Certain amino acid side chains have the ability to accept or donate protons (Asp, Glu, His*, Lys, Arg, Ser) d. Covalent catalysis 1. The formation of a transient covalent bond between the enzyme and the substrate e. Electrostatic catalysis 1. Involves electrostatic interactions between certain amino acid side groups which stabilize charged intermediates (transition states) f. Metal ion catalysis 1. Mostly involved in electron transfer reactions Fe +3 + 1e- yield Fe +2 IV. Serine proteases. Class of proteases (enzymes that degrade proteins) that possess a serine (R side chain of CH 2 -OH) residue at their active site .
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A. Most well characterized serine proteases: 1. Chymotrypsin : Cleaves C’ to aromatics A. Serine proteases are generally synthesized as ZYMOGENS:
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This note was uploaded on 11/04/2011 for the course BIOL 430 taught by Professor Lspremulli during the Fall '08 term at UNC.

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Chapter 6_1 - III. Catalytic Mechanisms: factors...

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