Lecture 20-22 - Lecture 20-22: Enzyme & Kinetics...

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Lecture 20-22: Enzyme & Kinetics Mechanisms of Catalysis 1. All chemical reactions, catalyzed or not, have a potential energy barrier a. Reaction can’t proceed until activation energy is available (applied with increased heat or pressure) b. The body at 37 C cannot overcome the potential energy barrier associated with many reactions c. Thus: Enzymes serve to lower the potential energy barrier to the transition state – such that the rxn requires a lower energy of activation i. Transition state is NOT an intermediate and can’t be isolated, rather it’s an energetic state 2. Enzymes don’t change the thermodynamics of a reaction a. G of the reaction is unchanged, only the pathway leading to a lower energy of activation is changed btw the catalyzed and uncatalyzed reaction 3. Due to induced fit of substrate and reaction intermediates, substrates or inhibitors that resemble transition or reaction intermediaries bind very tightly to the enzyme. Inhibitors = transition state analogs Enzymes Decrease the activation energy by: 1. Acid-base catalysis 2. Substrate strain (transition state stabilization) 3. Covalent catalysis 4. Entropy Effects Classes of Enzymes Class 1: Oxidoreductases – catalyze oxidative reduction reactions (alcohol dehydrogenases convert alcohols to aldehydes + 2 e - ) 1. Dehydrogenase: Transfers 2 electrons to NAD(P)+ 2. Oxidase : Transferes 2 electrons to molecular oxygen forming H 2 O2 2 3. Reductase : Transfers 2 electrons to NAD(P)+ 4. Peroxidase : Hydrogen Peroxide = electron acceptor 5. Catalas : Hydrogen peroxide = electron donor and receiver 6. Oxygenase: catalyze the incorporation of oxygen into a substrate 7. Hydroxylase: catalyze the incorporation of oxygen into a substrate, but a reduced cofactor is the electron donor
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1. Dehydrogenase – transfer 2 electrons to NAD(P)+
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This note was uploaded on 11/20/2011 for the course NS 3200 at Cornell University (Engineering School).

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Lecture 20-22 - Lecture 20-22: Enzyme & Kinetics...

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