How do competitive inhibitors affect enzyme activity?

• A. They decrease both Km and Vmax
• B. They increase Km without affecting Vmax
• C. They have no effect on Km or Vmax
• D. They decrease Vmax without affecting Km

Answer: (B)

Competitive inhibitors affect enzyme activity by binding to the active site of the enzyme, which prevents substrates from binding. This alters the dynamics of how the enzyme interacts with the substrate, specifically influencing the Km value.

In the presence of a competitive inhibitor, more substrate is required to reach half of the maximum reaction rate (Vmax). This is reflected in an increased Km value, which indicates a decreased affinity of the enzyme for its substrate. However, the Vmax remains unchanged, because if sufficient substrate is available, it can outcompete the inhibitor for binding to the active site, allowing the reaction to proceed at its maximum rate.

Thus, the correct answer highlights that competitive inhibition increases Km without affecting Vmax, demonstrating a key principle of enzyme kinetics. Understanding this concept is essential for grasping how enzymes operate under various conditions and how drugs may modulate these activities.