Enzyme Inhibitors

• Enzyme Inhibitors


  Substances that reduce or stop enzyme activity
• Reversible inhibitors


  • Can temporarily reduce or stop an enzyme's activity
• Types of reversible inhibitors

  • Competitive inhibitors
  • Non-competitive inhibitors
• Competitive inhibitors


  Have a similar shape to the substrate and compete with it for the active site
• Non-competitive inhibitors


  Bind to an alternative site on the enzyme, altering the shape of the active site and preventing substrate binding
• Increasing inhibitor concentration


  Reduces the rate of reaction, eventually stopping it completely
• Increasing substrate concentration for competitive inhibitors

  Can increase the rate of reaction again
• Increasing substrate concentration for non-competitive inhibitors

  Cannot increase the rate of reaction
• End-product inhibition


  Reversible inhibitors can act as regulators in metabolic pathways by using the end-product as a non-competitive inhibitor
• End-product inhibition process


  1. Enzyme converts substrate into product

  2. End-product binds to alternative site, changing active site shape

  3. End-product detaches, allowing active site to reform

  4. Enzyme catalyses reaction again
• Non-reversible inhibitors


  Form covalent bonds with enzymes, inhibiting them permanently
• Non-reversible inhibition can completely inactivate an enzyme, causing the biological reaction to stop completely</b>
• The only way to avoid this is for the cell/organism to produce more of the inhibited enzyme, which is a slow process
• Non-reversible inhibitors are considered metabolic poisons
• Non-reversible inhibitors


  • Cyanide
  • Lead
  • Mercury
• Cyanide


  Non-reversible inhibitor of cytochrome oxidase, a key enzyme in aerobic respiration
• Lead


  Non-reversible inhibitor of ferrochelatase, an enzyme involved in haemoglobin production
• Some non-reversible inhibitors can be beneficial in a medical context to inhibit harmful enzymes
• Medicinal non-reversible inhibitors


  • Penicillin
  • Aspirin
  • Eflornithine
• Penicillin


  Non-reversible inhibitor of transpeptidase, an enzyme that helps form bacterial cell walls