Enzyme inhibitors Flashcards
How can inhibitors be applied for drug design?
- ID target enzyme
- Find a compound that affects the target enzyme
- Characterize enzyme-inhibitor interactions
- Optimize the inhibitor to be developed into a drug
What are competitive inhibitors?
Inhibitors that mimic the substrate and compete with it for the active site
Can you swamp out a competitive inhibitor by adding more substrate?
Yes
What is apparent Km?
Uninhibited Km times alpha. Alpha is 1 + [I]/Ki
What is Ki?
Constant for inhibitor binding, which is Ki = [E][I]/[EI]
Does a competitive inhibitor affect the y-intercept?
No effect
Does a competitive inhibitor affect Vmax?
No effect
Does a competitive inhibitor affect slope?
Increases
Does a competitive inhibitor affect Km?
Increases
What are uncompetitive inhibitors?
Inhibitors that bind to allosteric sites in the enzyme-substrate complex, which inactivates it and doesn’t allow the reaction to proceed
Can you swamp out an uncompetitive inhibitor?
No
Does an uncompetitive inhibitor affect the y-intercept?
Increases
Does an uncompetitive inhibitor affect Vmax?
Decreases
Does an uncompetitive inhibitor affect slope?
No change
Does an uncompetitive inhibitor affect Km?
Decreases proportionally to Vmax
What is mixed inhibitor?
Binds to a site that exists either on the free enzyme or the enzyme-substrate complex and inactivates it
Can you swamp out a mixed inhibitor?
No
What does the Dixon plot look like for a mixed inhibitor?
The lines intersect before the Y-axis
Does a mixed inhibitor affect the y-intercept?
Increases
Does a mixed inhibitor affect Vmax?
Decreases
Does a mixed inhibitor affect the slope?
Increases
Does a mixed inhibitor affect Km?
Can either increase or decrease depending on where the lines intersect
What special type of inhibitors has the lines of the Dixon plot intersect on the x-axis?
Non-competitive inhibitor
What happens to Km for a non-competitive inhibitor?
No change, since alpha and alpha’ are the same
What are transition state analogs?
Molecules that mimic the transition state of an enzyme
How do transition state analogs work?
They bind really strongly to the enzyme in the active site by mimicking the transition state, but don’t react
How is an irreversible inhibitor different from a reversible inhibitor?
They bind covalently to the enzyme and can’t dissociate which results in permanent inactivation, while a reversible inhibitor uses non-covalent interactions
How do mechanism-based irreversible inhibitors work?
The enzyme gets inactivated partway through the reaction, so the reaction doesn’t go to completion
How does fluorouracil work as an irreversible inhibitor?
It inhibits thymidylate synthase by looking like a thymine, but has a fluorine at the position on thymine that reacts. The enzyme can’t pull off the fluorine so it stops
