An enzyme assay is repeated with an inhibitor added. As inhibitor concentration rises, both the measured Km and the measured Vmax decrease proportionally. The inhibitor binds only to the enzyme-substrate complex, not the free enzyme. Which type of inhibition is this?

• A Competitive inhibition
• B Pure noncompetitive inhibition
• C Mixed inhibition
• D Uncompetitive inhibition ✓

Explanation

Uncompetitive inhibitors bind exclusively to the ES complex, forming an inactive ESI complex. This removes ES from equilibrium, paradoxically increasing apparent substrate affinity, so Km falls, while Vmax also falls because productive complexes cannot release product. The hallmark is a proportional decrease in both parameters with parallel Lineweaver-Burk lines. Mixed inhibition raises or leaves Km unchanged while lowering Vmax because it binds both E and ES, which is explicitly excluded here.

Reference: Lehninger Principles of Biochemistry, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.