Question

Which of the following is true for competitive enzyme inhibition?

• A. Decrease in $V_{max}$ and $K_m$
• B. Unchanged $V_{max}$ and decrease in $K_m$
• C. Unchanged $V_{max}$ and increase in $K_m$
• D. Increase in $V_{max}$ and $K_m$

Answer 1

The correct option is C Unchanged $V_{max}$ and increase in $K_m$

$V_{max}$ is maximum velocity of the enzyme. The Michaelis constant (K${}_m$) is defined as the substrate concentration at which the reaction rate is half of its maximal value.

Competitive inhibitors can only bind to enzyme [E] and not to enzyme substrate complex [ES]. They increase $K_m$ by interfering with the binding of the substrate, but they do not affect $V_{max}$ because the inhibitor does not change the catalysis in ES because it cannot bind to ES. Hence, $V_{max}$ remains same and $K_m$ increases in competitive inhibition.