2.4 Enzyme inhibition Flashcards
Define what is an inhibitor?
Inhibitor - substance that decreases the rate of enzyme catalysed reaction
What are the two main classes of enzyme inhibitors?
Reversible - temporarily (transiently) bind to enyzmes, are later released
Irreversible - dissociate slowly from the enzyme because strongly bound / change the conformation of the enzyme
What are the types of enzyme inhibition?
- Competitive
- Uncompetitive
- Non-competitive
Explain competitive inhibition
Competitive inhibition:
- inhibitor binds to the same active site as S - structurally very similar - they compete for the enzyme
- if [S] is increased a lot - Vmax of enzyme can still be reached if the inhibitor is outcompeted
- Km will be higher (more S needed to fill 1/2 of active sites) because competition is imposed
Explain non-competitive inhibition
Non-competitive inhibition:
- S and inhibitor (allosteric site) bind to different sites on the enzyme
- Vmax will be decreased because inhibitor binding can’t be stopped
- Km ([S] which fills 1/2 active sites) will remain the same because only S will bind to the active site
Explain uncompetitive inhibition
Uncompetitive inhibition:
- inhibitor binds after the substrate has bound to the enzyme (to ES complex)
- Vmax will decrease - although S binds, no product formed due to inhibition
- Km will decrease because inhibitor will create a ‘tighter ES complex binding effect’ (ES held together affects equilibrium - less [S] needed for 1/2 of active sites)
Why non-competitive inhibition can be viewed as mixed inhibition?
- competitive side: inhibitor can only bind if S not bindinded (as if competition for active site)
- uncompetitive side: but it doesn’t use the same active site as S - not competing for the same active site
Inhibition mechanism summary
Explain mixed inhibiton mechanism
- Mixed inhibition - combination of mechanisms (ex: inhibitor can act in both competitive and uncompetitive manner)
