• An enzyme's activity can be reduced or stopped, temporarily, by a reversible inhibitor
• There are?two types?of reversible inhibitors:
  • Competitive?inhibitors have a?similar shape?to that of the?substrate?molecules and therefore?compete?with the substrate for the active site
  • Non-competitive?inhibitors?bind?to the enzyme at an?alternative site, which?alters the shape of the active site?and therefore?prevents?the?substrate?from?binding?to it

Competitive and non-competitive inhibition

• Reversible inhibitors can act as?regulators?in?metabolic pathways
• Metabolic reactions must be very?tightly controlled?and?balanced, so that no single enzyme can ‘run wild’ and continuously and uncontrollably generate more and more of a particular product
• Metabolic reactions can be?controlled?by using the?end-product?of a particular sequence of metabolic reactions as a?non-competitive, reversible inhibitor:
  • As the enzyme converts substrate to product, the process is itself?slowed down?as the?end-product?of the reaction chain binds to an alternative site on the original enzyme, changing the shape of the active site and preventing the formation of further enzyme-substrate complexes
  • The end-product can then?detach?from the enzyme and be used elsewhere, allowing the active site to?reform?and the enzyme to return to an?active state
  • This means that as product levels fall, the enzyme begins catalysing the reaction once again, in a continuous?feedback loop
  • This process is known as?end-product inhibition

End-product inhibition