Enzyme Inhibitors (Cambridge International A-Level Biology)

Spec point — 3.2.3 · explain the effects of reversible inhibitors, both competitive and non-competitive, on enzyme activity

Enzyme inhibitors

• 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

    • This means they 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

    • This prevents the substrate from binding to it

*Competitive and non-competitive inhibition by reversible inhibitors *

• 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 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's shape 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