MCAT® ExamBiological and Biochemical Foundations of Living SystemsMedium
A researcher is studying a newly discovered enzyme that catalyzes a crucial step in a metabolic pathway. They observe that the enzyme's activity is significantly reduced in the presence of a molecule that binds to a site distinct from the active site, inducing a conformational change that lowers the enzyme's affinity for its substrate. This type of regulation is best described as:
- ANon-competitive inhibition
- BCompetitive inhibition
- CAllosteric activation
- DUncompetitive inhibition
Show answer & explanationAnswer & explanation
Correct answer: A. Non-competitive inhibition
Non-competitive inhibition occurs when an inhibitor binds to an allosteric site on the enzyme, separate from the active site. This binding causes a conformational change that reduces the enzyme's efficiency, specifically lowering its Vmax, without necessarily affecting substrate binding (Km).
Why the other options are wrong
- B. Competitive inhibition involves an inhibitor binding to the active site, directly competing with the substrate.
- C. Allosteric activation would increase enzyme activity, not reduce it, by binding to an allosteric site.
- D. Uncompetitive inhibition involves an inhibitor binding only to the enzyme-substrate complex.
Non-competitive Inhibition
A type of enzyme inhibition where the inhibitor binds to an allosteric site on the enzyme, not the active site. This binding induces a conformational change that reduces the enzyme's catalytic efficiency (Vmax) without affecting the substrate's ability to bind (Km).
- Inhibitor binds to an allosteric site.
- Does not compete with substrate for the active site.
- Decreases Vmax (maximum reaction rate).
- Km (substrate affinity) remains unchanged.
Memory trick: Don't Compete, Just Non-Competitively Change the Game.