An enzyme with Km = 2 mM and Vmax = 100 nmol/min is inhibited by a competitive inhibitor at concentration 5 mM with Ki = 1 mM. The apparent Km in the presence of the inhibitor is:

• A 4 mM
• B 12 mM ✓
• C 2 mM (unchanged)
• D 10 mM

Explanation

For competitive inhibition, apparent Km = Km × (1 + [I]/Ki) = 2 × (1 + 5/1) = 2 × 6 = 12 mM. Vmax is unchanged because excess substrate can overcome competitive inhibition. The Lineweaver-Burk plot shows lines intersecting on the y-axis (1/Vmax unchanged) with increased x-intercept (−1/Km shifts left toward zero). This distinguishes competitive from uncompetitive inhibition, where both apparent Km and Vmax decrease by the same factor.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.