An enzyme shows a Km of 5 mM and Vmax of 100 nmol/min. A new compound doubles the apparent Km to 10 mM without changing Vmax. A Lineweaver-Burk plot of the inhibited reaction would show:

• A Lines intersecting on the X-axis (same Km, decreased Vmax) — consistent with uncompetitive inhibition
• B Parallel lines shifted to the right of the control line — consistent with uncompetitive inhibition
• C Lines intersecting to the left of the Y-axis with a decreased Y-intercept — consistent with mixed inhibition
• D Lines intersecting on the Y-axis (same Vmax, increased Km) — consistent with competitive inhibition ✓

Explanation

Competitive inhibition increases apparent Km without changing Vmax. On a Lineweaver-Burk double-reciprocal plot (1/v vs 1/[S]), the inhibited line has a steeper slope (higher Km) but the same Y-intercept (same 1/Vmax), so the two lines intersect on the Y-axis. Uncompetitive inhibition produces parallel lines (increases both apparent Km and decreases apparent Vmax proportionally). Mixed/noncompetitive inhibition lines intersect to the left of the Y-axis. Competitive inhibitors compete with substrate for the active site and can be overcome by high substrate concentrations.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.