In a Lineweaver–Burk plot, a competitive inhibitor shows which change in Vmax and Km?

In a Lineweaver–Burk plot, a competitive inhibitor shows which change in Vmax and Km?

• A. Same Vmax, higher Km
• B. Lower Vmax, same Km
• C. Lower Vmax, lower Km
• D. Higher Vmax, higher Km

Answer: (A)

Competitive inhibition affects how the substrate binds: the inhibitor competes with the substrate for the active site, so the apparent substrate affinity decreases (Km increases). However, the maximum rate is still attainable if the substrate is high enough, so Vmax remains unchanged. In a Lineweaver–Burk plot (1/v vs 1/[S]), the y-intercept represents 1/Vmax and the x-intercept represents -1/Km. Since Vmax is unchanged, the lines all cross the same y-intercept, but Km has increased, shifting the x-intercept toward zero. This pattern is why the correct description is the same Vmax with a higher Km.

Competitive inhibition affects how the substrate binds: the inhibitor competes with the substrate for the active site, so the apparent substrate affinity decreases (Km increases). However, the maximum rate is still attainable if the substrate is high enough, so Vmax remains unchanged.

In a Lineweaver–Burk plot (1/v vs 1/[S]), the y-intercept represents 1/Vmax and the x-intercept represents -1/Km. Since Vmax is unchanged, the lines all cross the same y-intercept, but Km has increased, shifting the x-intercept toward zero. This pattern is why the correct description is the same Vmax with a higher Km.