• stop enzymes working
  • decrease rate of reaction
  • block active sites

An inhibitor is any substance that slows down the rate of an enzyme controlled reaction by affecting the enzyme molecule.

Competitive Inhibitors

  • Similar shape to substrate
  • Occupy active sites
  • Form enzyme-substrate inhibitor complexes
  • Enzyme-substrate complex decreases rate of reaction
  • Level of inhibition depends on concentration of substrate/inhibitor
  • most don’t bind permanently, making the reaction reversible

Alcohol Dehydrogenase and ethylene glycol

  • An ethylene glycol overdose can be fatal
  • In the liver, it is broken down into oxalic acid (very toxic) by alcohol dehydrogenase
  • By administering a large dose of ethanol, you can prevent oxalic acid production by filling all active sites with a competitive substance.

Non-competitive Inhibitors

  • Bind elsewhere on the enzymes
    • Alosteric site
  • Affects the tertiary structure leading to a change in the shape of the active site
  • Level of inhibition depends on concentration of inhibitor
  • Many bind permanently, making the reaction irreversible

Protein Pump Inhibitors (PPIs)

  • Stomach acidity is determined by H⁺ ion concentration
  • Inhibiting the pumps reduces H⁺ ion production
  • Which increases the pH of stomach acid
  • Leading to lower acidity
  • A PPI binds to an alosteric site and changes the tertiary shape of the enzyme, preventing the complementary substrate from binding

End production inhibition

  • Product of one reaction is an inhibitor to the enzyme that produced it.

Biochemical reactions

  • Products of one reaction becomes substrate for the next
  • One product may inhibt the enzyme that produced it, limiting the rate of reaction and creating a negative feedback loop