Chapter_10

Chapter_10 - Chapter 10 Enzyme Regulatory Strategies 1 2 3...

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Chapter 10 Enzyme Regulatory Strategies 1. Allostery-Hemoglobin & Aspartate Transcarbamylase (ATC) 2. Isozymes-same reaction, different structure 3. Covalent modification, protein kinase 4. Proteolytic activation, irreversible modification
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Chapter 10 Please read 275-282, 283-290, 292-296
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Feedback (end-product) Inhibition in ATCase Inhibitor is  structurally  different from  substrates Allo- “other” Stereo- “structure” c=catalytic, r=regulatory Hg compound  dissociates subunits Mercaptoethanol  removes compound Separation by ion-exchange or centrifugation 11.6S, 2.8S Enzyme activity can be regenerated!
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ATCase is a multimer Contacts between 2 catalytic trimers Each r chain interacts w. a c chain 2c3 + 3r2 c6r6
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PALA mimics reaction intermediate  and binds into active site Each PALA contacts  2 c subunits Boxed residues come from 2nd subunit Mechanism of Allosteric Regulation is Revealed by PALA Bound  Structure 3 binding sites per trimer
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The All or None (“Concerted”) Allosteric Mechanism Catalytic trimers move 12   apart Ǻ Single CTP  binding site in  each r subunit 50   between CTP  Ǻ and active site
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Kinetics of Allosteric Enzymes are Modulated by Regulator Molecules Cooperativity is indicated by  “S” shape Homotropic: effect  of substrate Heterotropic: effect  of other regulators Isolated catalytic trimer  and r dimer exhibit  michaelis-menten  kinetics Isolated c subunit ATP stabilizes “R” state CTP stabilizes “T” state
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R T L = [T]/[R] SiteR + S           SiteR - S SiteT + S           SiteT - S KR = [SiteR][S]/[SiteR – S] KT = [SiteT][S]/[SiteT – S]
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Chapter_10 - Chapter 10 Enzyme Regulatory Strategies 1 2 3...

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