Question

For an enzyme that follows Michaelis-Menten kinetics, a competitive inhibitor

• A. increases both \( K_m \) and \( V_{{max}} \)
• B. decreases both \( K_m \) and \( V_{{max}} \)
• C. increases \( K_m \) but does not affect \( V_{{max}} \)
• D. decreases \( K_m \) but does not affect \( V_{{max}} \)

Hint:

In competitive inhibition, \( V_{{max}} \) remains the same, but \( K_m \) increases because the inhibitor reduces the enzyme's affinity for the substrate, requiring higher substrate concentrations to achieve the same rate.

Answer 1

The Correct Option is C

In competitive inhibition, the inhibitor competes with the substrate for binding to the enzyme's active site. As a result, more substrate is required to reach half of the maximum reaction rate, which increases the Michaelis constant (\( K_m \))—a measure of substrate affinity. However, the maximum reaction rate (\( V_{{max}} \)) remains unchanged because the inhibitor can be outcompeted by increasing substrate concentration. Thus, statement (C) is correct.
- (A): Competitive inhibition increases \( K_m \) but does not affect \( V_{{max}} \). Therefore, statement (A) is incorrect.
- (B): Competitive inhibition does not decrease \( V_{{max}} \), as increasing substrate concentration can overcome the inhibition. Hence, statement (B) is incorrect.
- (D): Competitive inhibition increases \( K_m \), not decreases it. Therefore, statement (D) is incorrect.
Thus, the correct answer is (C).