Feedback Inhibition

• Feedback inhibition


  A form of negative feedback by which metabolic pathways can be controlled
• End-product inhibition


  In end-product inhibition, the final product in a series of reactions inhibits an enzyme from an earlier step in the sequence
• End-product inhibition


  1. The product binds to an allosteric site

  2. Temporarily inactivates the enzyme (via non-competitive inhibition)

  3. Reaction sequence is halted

  4. Rate of product formation is decreased
• If product levels build up

  The product inhibits the reaction pathway and hence decreases the rate of further product formation
• If product levels drop

  The reaction pathway will proceed unhindered and the rate of product formation will increase
• Isoleucine


  An essential amino acid, meaning it is not synthesised by the body in humans (and hence must be ingested)
• Food sources rich in isoleucine


  • eggs
  • seaweed
  • fish
  • cheese
  • chicken
  • lamb
• Isoleucine synthesis pathway in plants and bacteria


  1. Threonine is converted into an intermediate compound by an enzyme (threonine deaminase)

  2. Isoleucine can bind to an allosteric site on this enzyme and function as a non-competitive inhibitor
• Excess production of isoleucine


  Inhibits further synthesis
• This feedback inhibition ensures that isoleucine production does not cannibalise available stocks of threonine