Enzyme Inhibitors

• Inhibitors are substances that reduce enzyme activity by interfering with the active site; types: competitive and non-competitive
• Non-Competitive Inhibitors: Dissimilar shape to substrate; don’t bind to active site, but to the allosteric site; cause the tertiary structure (and active site) to change shape, substrate can no longer bind, many are irreversible and bind permanently (e.g. heavy metal ions like lead, silver, mercury, and copper ions)
• Non-Competitive Inhibitors: Depends only on the concentration of the inhibitor, if there are enough to attach to all enzyme allosteric sites, the reaction will stop, increasing substrate concentration will not impact; they are not competing for the same sites
• End-product Inhibition: Sometimes inhibition is desirable to regulate/control metabolic pathways; end product always binds to the allosteric site to act as a reversible non-competitive inhibitor
• Reversible Inhibitors: Use weaker hydrogen bonds or ionic bonds, easy to remove and Non-reversible Inhibitors: Strong covalent bonds, not easy to remove
• Graph 1

  A) No Inhibitor

  B) Non-Competitive Inhibitor

  C) Non-Competitive

  
• Graph 2

  A) Competitive Inhibitor

  B) No Inhibitor

  C) Competitive

  
• Competitive Inhibitors: Similar shape to substrate, so they can occupy the active site; but for a short time (reversible), when they bind but no reaction takes place, the active site is blocked; effect of these inhibitors depends upon the concentrations of the inhibitor and substrate, if substrate concentration is increased, the inhibition will be reduced