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Enzymes – protein catalysts

Enzymes – protein catalysts. The active site can lower an E A barrier by orienting substrates correctly straining substrate bonds providing a favorable microenvironment directly participating in the reaction. Induced Fit of Substrate e.g. carboxypeptidase. Substate. Active site.

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Enzymes – protein catalysts

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  1. Enzymes – protein catalysts • The active site can lower an EA barrier by • orienting substrates correctly • straining substrate bonds • providing a favorable microenvironment • directly participating in the reaction

  2. Induced Fit of Substratee.g. carboxypeptidase

  3. Substate Active site Enzyme- substrate complex (b) Enzyme (a)

  4. Zn2+ - an essential cofactor in carboxypeptidase

  5. Mechanism of action

  6. A substrate can bind normally to the active site of an enzyme. Substrate Active site Enzyme (a) Normal binding A competitive inhibitor mimics the substrate, competing for the active site. Competitive inhibitor (b) Competitive inhibition Competitive inhibitors • Bind to the active site of an enzyme, competing with the substrate

  7. A noncompetitive inhibitor binds to the enzyme away from the active site, altering the conformation of the enzyme so that its active site no longer functions. Noncompetitive inhibitor (c) Noncompetitive inhibition Figure 8.19 Noncompetitive inhibitors • Bind to another part of an enzyme, changing the function

  8. Examples of allosteric regulation: -phosphorylation -Ca2+/calmodulin

  9. Initial substrate(threonine) Active siteavailable Threoninein active site Enzyme 1(threoninedeaminase) Isoleucineused up bycell Intermediate A Feedbackinhibition Enzyme 2 Active site of enzyme 1 no longer binds threonine;pathway is switched off Intermediate B Enzyme 3 Intermediate C Isoleucine binds to allosteric site Enzyme 4 Intermediate D Enzyme 5 End product(isoleucine)

  10. Cellular Respiration C6H12O6 + O2↔ 6CO2 + 6H2O forward reaction: DG = -686 kcal/mol reverse reaction: DG = 686 kcal/mol

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