Inhibitors

• An inhibitor is a substance which slows down or stops a reaction by affecting the binding of substrate to the enzymes. Inhibitors can either be reversible and irreversible.
• What are examples of irreversible inhibitors?

  Heavy metal ions

  Cyanide
• How does a heavy metal ion inhibit enzyme function?

  They cause disulphide bonds within the protein structure to break, as a result causing the shape of the active site to change, thus affecting protein activity.
• How does cyanide affect enzyme activity?

  Cyanide is a nerve gas that covalently binds to the active site, therefore preventing the binding of the substrate.
• Reversible inhibitors bind to the active site through hydrogen bonds and weak ionic

  interactions therefore they do not bind permanently.
• What are the two types of reversible inhibitors?

  Competitive

  Non-competitive
• Competitive inhibitors are similar in structure to the substrate molecule therefore they bind to the active site of the enzyme, decreasing its activity as they compete with substrate for the enzyme.
• In an enzyme inhibited by competitive inhibitors, the amount of product formed remains the same, however the rate at which product formation occurs decreases.
• The higher the concentration of competitive inhibitor the

  lower the reaction rate. Increasing the substrate reverses the effect of competitive inhibitors

  by outcompeting them.
• Non-competitive inhibitor does not bind to the active site; it binds at another site on the enzyme known as the allosteric site.
• Binding of the non-competitive inhibitors changes the shape of the active site therefore preventing the binding of the substrate. Increasing the concentration of substrate has no effect on non-competitive inhibition.
• What are examples of drugs which are inhibitors?

  Penicillin

  Ritonavir
• How is penicillin an inhibitor?

  Penicillin which is used to fight bacterial

  infections, it is an inhibitor of enzyme transpeptidase which plays an important role in cell wall formation.
• how is ritonavir an inhibitor?

  Ritonavir which is an antiretroviral drug used to treat HIV which inhibits HIV protease which is responsible for assembly of new viral particles and spread of infection.