4.3 Enzyme inhibitors

4.3 Enzyme inhibitors

1. Competitive inhibition

   • How it works
     • A molecule that has a similar shape to the substrate can fit into the active site
     • This prevents the substrate from enterring the active site - hence the enzyme can't carry out its function
     • The substrates and inhibitors compete to bind with the enzyme, therefore reduce the rate of reaction
     • Most competitive inhibitors only temporarily bind so the reaction is reversable. However some are permanent such as aspirin
   • Effect on rate of reaction
     • A competitive inhibitor reduces the rate of reaction but doesnt change the V-max
   • Examples of competitive inhibition
     • Statins- are competitive inhibitors in cholesterol synthesis
     • Aspirin - irreversably inhibits cox enzymes and therefore reduces pain.

2. Non competitive inhibitors

   • How it works
     • Inhibitor binds to enzyme at the allosteric site (alternative site to active site
     • This binding causes the tertiary structiure to change shape, hence changing the shape of the active site
     • Consequently the active site is no longer complimentary to the substrate
     • These inhibitors don't compete for the active site, therefore its non competitive
   • Effects on rate of reaction
     • Increasing the conc of enzyme/substrate won't overcome a non-competitive inhibitor. However increasing the conc of the inhibitor will reduce the rate of reaction

3. End product inhibition

   • End product inhibition is the term used for enzyme inhibition that occurs when the product of a reaction acts as an inhibitor to the enzyme that produces it. This is a negative feedback mechanism
   • Example in respiration
     • 1-Glucose is broken down by the addiition of 2 phosphate groups, the addition of the 2nd phosphate breaks down the glucose
     • 2- Therefore when the ATP levels are high and more ATP to the allosteric site preventing the addition of the 2nd phosphate. hence glucose isn,t broken down.
     • 3- Then as ATP is used less binds to the enzymes and they can now catalyse the reaction and produce more ATP.