Enzyme inhibitors Flashcards
What are inhibitors
bind to an enzyme and decrease its activity.
What are the types of inhibitors (2)
- Irreversible
- Reversible - medicines to target enzymes
What are the types of reversible inhibitors (3)
- Uncompetitive inhibitors
- Competitive inhibitors
- Non-competitive inhibitors
What happens with uncompetitive inhibition (3)
- After ES binding - Binds to ES
- ES locked in so KM & Vmax is lowered
- High [S] = some ESI bound
What happens with competitive inhibition (4)
- Substrate and Inhibitor compete for the active site
- Bind to E forming EI at the expense of ES
- KM increases as more substrate is needed to reach half Vmax (reaction rate)
- High [S] = no Vmax effect, as more [S] = overwhelmed Enzyme and competition can be won by S
What happens with allosteric regulation (6)
- Effector molecule binds at
a site other than active site. - Changes activity (+/-) depending on binding molecule
- Non-competitive inhibition
- regulation via a control loop
- +/- feedback from downstream products
- +/- feedforward from upstream substrates.
What happens with non-competitive inhibition (3)
- Not picky so binds to E & ES
- Allosteric binding = few working enzymes = lower Vmax (rate)
- Substrate can still bind to active site = KM staying the same
What are Lineweaver-Burk (LB) plots used for
distinguish between inhibitor types at different [I]
What effect do competitive inhibitors have on Vmax and KM according to Lineweaver-Burk (LB) plots
Vmax = stays the same
Km = increases
What effect do uncompetitive inhibitors have on Vmax and KM according to Lineweaver-Burk (LB) plots
Vmax = decreases
KM = decreases
What effect do non-competitive inhibitors have on Vmax and KM according to Lineweaver-Burk (LB) plots
Vmax = decreases
KM = stays the same
What happens with pure non-competitive inhibition (4)
- Mixed inhibition due to different affinities for E & ES allosteric sites
- Substrate = same affinity for E & EI (active site still available, allosteric binding)
- Greater affinity for E = more like competitive
- Greater affinity for ES = more like uncompetitive
