In a double-reciprocal (Lineweaver-Burk) plot, an inhibitor causes the lines at different inhibitor concentrations to intersect ON the x-axis (same x-intercept = same -1/Km, different y-intercepts). This inhibitor type is:

• A Competitive inhibitor ✓
• B Uncompetitive inhibitor
• C Non-competitive (pure) inhibitor
• D Mixed inhibitor

Explanation

In a Lineweaver-Burk plot, the x-intercept = -1/Km and the y-intercept = 1/Vmax. A competitive inhibitor increases the apparent Km (because the inhibitor competes with substrate at the active site; more substrate overcomes it) but does NOT change Vmax. Thus the y-intercept changes (increased 1/Vmax app meaning lines have different slopes) while the x-intercept is the same (same Km app only when using different formulations — actually: lines intersect at the x-axis meaning same -1/Km). This confirms a competitive pattern: Km increases (x-intercept more negative or converges at x-axis), Vmax unchanged.

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

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Written and medically reviewed by the StethoPrep medical team.