More substrate only beats a competitive inhibitor
- The idea
- Predict
- See it
- Why
- Check
The idea
“More substrate can overcome a noncompetitive inhibitor, but a competitive one stays strong.”
"Competitive" sounds like the inhibitor that always wins. It actually fights substrate for the same spot, and it loses when substrate floods in.
The short version
The mistake: More substrate can overcome a noncompetitive inhibitor, but a competitive one stays strong.
What's actually true: Extra substrate crowds a competitive inhibitor out of the active site. A noncompetitive inhibitor keeps the top rate low.
- A competitive inhibitor binds the active site, where substrate binds. With enough substrate, substrate holds that site most of the time.
- So the enzyme gets close to its normal top rate again. It just needs more substrate to get there.
- A noncompetitive inhibitor binds a different spot, an allosteric site. It changes the enzyme's shape so the active site works poorly.
- Substrate can't push it off, so the top rate stays low however much substrate you add.
On the exam: Add lots of substrate. If the rate climbs back near normal, it's competitive. If not, it's noncompetitive.