Enzyme Inhibitors

• what are inhibitors?

  reduce the rate of enzyme-controlled reactions
• what are the two main types of enzyme inhibitors?

  • competitive inhibitor
  • non-competitive inhibitor
• what are competitive inhibitors?

  • have a similar shape to substrate molecule, they occupy the active site forming and enzyme-inhibitor complexes, which do not lead to the formation of products - so compete for binding in active site
  • substrate molecule can’t enter the active site, so the number of enzyme-substrate complexes is reduced, therefore reducing rate of reaction
• what does the amount of inhibiton depend on?

  the relative concentration of substrate and inhibitor molecules - more inhibitor molecules means more inhibitors collide with active sites and so the effect of inhibitor is greater
• what kind of Vmax do competitive inhibitors have?

  the same Vmax as a normal enzyme, just a slower rate of reaction
• what is a non-competitive inhibitor?

  • they reduce rate of reaction
  • do not compete with substrate molecules to binds to the active site
  • they binds to a region away from active site
  • this can distort the tertiary structure of the enzyme, leading to a change in shape of the enzyme
  • this means the substrate is no longer complementary to active site so cannot bind, enzyme-substrate complexes cannot form so the reaction rate decreases
• what is the active site also called?

  allosteric site
• what kind of Vmax do non competitive inhibitors have?

  they have a lower Vmax and a slower rate of reaction
• what is meant by end-product inhibition?

  • many metabolic processes consist of a series of enzyme-controlled reactions
  • the product of the first reaction is the substrate of the second reaction
  • it is important that large quantities of the final end product (and the intermediate molecules) do not accumulate as this would be wasteful
  • the end product acts as a reversible non-competitive inhibitor to one of the enzymes early in the pathway - end product binds to allosteric site causing a change in shape so substrate no longer binds and reaction stops
• why is the inhibition of enzyme activity important in controlling metabolic processes?

  prevents the production of too much of a product - especially if product is toxic (amino acids)
• what is the difference between temporary and permanent inhibition?

  • temporary allows enzymes to return to original shape of active site and make more enzyme-substrate complexes
  • permanent prevents enzyme from returning to original shape as there is no way of removing inhibitor