An inhibitor increases the Km of an enzyme for its substrate without changing the Vmax. Increasing substrate concentration fully reverses the inhibition. This describes which type of inhibition?

• A Uncompetitive inhibition
• B Non-competitive inhibition
• C Irreversible inhibition
• D Competitive inhibition ✓

Explanation

Competitive inhibitors bind the active site and compete with substrate for the same site. They increase the apparent Km (reduce enzyme's affinity for substrate) because higher substrate concentrations are needed to displace the inhibitor. Vmax remains unchanged because at infinitely high substrate concentrations all enzyme molecules are substrate-bound. Excess substrate fully reverses competitive inhibition. On a Lineweaver-Burk (double-reciprocal) plot, competitive inhibitors increase the x-intercept (−1/Km moves toward zero) while the y-intercept (1/Vmax) is unchanged. Non-competitive inhibition decreases Vmax with unchanged Km. Uncompetitive inhibition decreases both Km and Vmax (parallel shift on LB plot).

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

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