Discussion
Researchers measure the activity of an enzyme in the presence of an inhibitor. They observe that
- Vmax of the enzyme remains unchanged at saturating substrate concentration
- Km increases compared to uninhibited enzyme
Which type of inhibition is most consistent with these observations?
Answer: A
The observations fit competitive inhibition.
A competitive inhibitor binds the free enzyme at the active site, competing with the substrate. Adding more substrate outcompetes it, so at saturating substrate the enzyme still reaches the same Vmax. But more substrate is needed to reach half that rate, so the apparent Km increases.
Pure non-competitive inhibition lowers Vmax and leaves Km unchanged, because the inhibitor binds enzyme and enzyme-substrate complex equally. An irreversible inhibitor removes active enzyme, which also lowers Vmax. Substrate inhibition is a fall in rate at very high substrate concentration, which is not what was seen.
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