2.8 Enzyme inhibition

2.8 Enzyme inhibition

1. COMPETITIVE INHIBITORS

   • Have molecular shape similar to substrate
     • Can occupy active site of enzyme
       • Compete with substrate
   • Concentration of inhibitor vs. concentration of substrate
   • Greater concentration of substrate = effect of inhibitor reduced
   • Not permanently bound to active site
     • Another molecule can take its place
       • Sooner or later, all substrate molecules will occupy active sites
         • The greater the inhibitor concentration, the longer this will take

2. NON-COMPETITIVE INHIBITORS

   • Attach to enzyme at a site other than the active site
     • Shape of active site is altered
       • Substrate molecules unable to bind to active site
   • Substrate and inhibitor not competing for active site
     • Increase in substrate concentration does not decreases effect of inhibitor

3. METABOLIC PATHWAYS

   • END-PRODUCT INHIBITION
     • End product inhibits enzyme 1
       • Quantity of end product increases above normal
         • Greater inhibition of enzyme 1
           • Less end product produced
             • Level returns to normal
       • Quantity of end product falls below normal
         • Decreased inhibition of enzyme 1
           • More end product produced
             • Level returns to normal
     • Level of any chemical maintained at relatively constant level
     • Non-competitive inhibition
   • A metabolic pathway is a series of reactions in which each step is catalysed by an enzyme.
     • To keep a steady level of a particular chemical, the same chemical often acts as an inhibitor of an enzyme at the start of a reaction

4. Enzyme inhibitors are substances that directly or indirectly interfere with the functioning of the active site of an enzyme and so reduce its activity.

   • Some inhibitors bind so strongly to the active site that it cannot be removed = permanently prevent enzyme functioning = IRREVERSIBLE INHIBITORS
   • Most inhibitors make temporary attachments to the active site = REVERSIBLE INHIBITORS
     • COMPETITIVE INHIBITORS - bind to active site of enzymes
     • NON-COMPETITIVE INHIBITORS - bind to enzyme at a position other than active site

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