Enzyme inhibitors

• Cellular conditions are at a narrow range - Enzyme activity is not delayed
• Reactions not happening too fast - Build up of excess products
• Inhibitors - Molecules that prevent enzymes from catalysing reactions
• 2 types of enzyme inhibition:

  • Competitive
  • Non-competitive
• Process of competitive inhibition:

  1. Molecules having similar shape to substrate binds to active site of the enzyme
  2. Substrate blocked from entering active site
  3. Enzyme can no longer carry out its function - Inhibited
• Competitive inhibition:

  • Substrate and inhibitor molecules compete to bind to active sites of enzymes
  • Number of substrate molecules binding to active sites reduced
  • Degree of inhibition depends on concentration of substrate, inhibitor and enzyme
• Competitive inhibition is reversible - Competitive inhibitors only bind temporarily to the active site

  • Asprin - exception
• Competitive inhibitors effect on rates of reaction:

  • Reduced rate of reaction for a concentration of substrate but enzyme Vmax not changed
  • Substrate concentration increased - More substrate than inhibitor - Original Vmax can be reached
• E.g. of competitive inhibition:

  Statin:

  • Synthesis of cholesterol

  Asprin:

  • Irreversible
  • COX enzymes
  • Prevent synthesis of molecules that produce pain and fever
• Process of non-competitive inhibition:

  1. Inhibitor binds to allosteric site - Alternative to active site
  2. Specific 3d tertiary changed due to binding of inhibitor
  3. Therefore active site changes shape - No longer complementary to substrate
  4. Substrate unable to bind to enzyme - Enzyme inhibited
• Non-competitive inhibitor- An inhibitor that does not compete with the substrate for the active site
• Effect on rate of reaction with non-competitive inhibitor:

  • Increase concentration of enzyme or substrate - Effect of non-competitive inhibitor not overcome
  • Increasing concentration of inhibitor - Decrease rate of reaction more - more active sites unavailable
• E.g. of irreversible non-competitive inhibitors:

  Organophosphates:

  inhibit acetyl cholinesterase - Affecting nerve impulse transmission

  Proton pump inhibitors:

  Inhibit enzyme responsible for secreting hydrogen ions into the stomach
• End-product inhibition - When the product of a reaction acts as an inhibitor to the enzyme that produces it
• End-product inhibition:

  • Negative feedback control mechanism
  • Excess products not wasted