enzyme inhibitors

• reversible inhibitors


  not bind permanently to an enzyme
• non-reversible inhibitors 


  bind permanently to an enzyme
• • If they're strong, covalent bonds, the inhibitor can't be removed easily and the inhibition is irreversible.
  • If they're weaker hydrogen bonds or weak ionic bonds, the inhibitor can be removed and the inhibition is reversible.
• Some antiviral drugs (drugs that stop viruses) are enzyme inhibitors - e.g. reverse transcriptase inhibitors are a class of antiviral developed to treat HIV. They work by inhibiting the enzyme reverse transcriptase, which catalyses the replication of viral DNA. This prevents the virus from replicating.
• Some antibiotics are enzyme inhibitors- e.g. penicillin inhibits the enzyme transpeptidase, which catalyses the formation of proteins in bacterial cell walls. This weakens the cell wall and prevents the bacterium from regulating its osmotic pressure. As a result the cell bursts and the bacterium is killed.
• Metabolic poisons interfere with metabolic reactions (the reactions that occur in cells), causing damage, illness or death - they're often enzyme inhibitors.
• Cyanide is a non-competitive, irreversible inhibitor of cytochrome c oxidase, an enzyme that catalyses respiration reactions. Cells that can't respire die.
• Malonate is a competitive inhibitor of succinate dehydrogenase (which also catalyses respiration reactions).
• Arsenic is a non-competitive inhibitor of pyruvate dehydrogenase, yet another enzyme that catalyses respiration reactions.
• end product inhibition 


  the final product in a metabolic pathway inhibits an enzyme that acts earlier on in the pathway
• Phosphofructokinase is an enzyme involved in the metabolic pathway that breaks down glucose to make ATP.

  ATP inhibits the action of phosphoructokinase - so a high level of ATP prevents more ATP from being made.
• Both product and end-product inhibition are reversible. So when the level of product starts to drop, the level of inhibition will start to fall and the enzyme can start to function again - this means that more product can be made.
• Enzymes are sometimes synthesised as inactive precursors in metabolic pathways to prevent them causing damage to cells. Part of the precursor molecule inhibits its action as an enzyme. Once this part is removed (e.g. via a chemical reaction) the enzyme becomes active.