Which description best characterizes competitive inhibition of enzymes?

Which description best characterizes competitive inhibition of enzymes?

• A. It binds to the allosteric site and decreases Vmax
• B. It binds irreversibly to the enzyme
• C. It binds to the active site, increasing apparent Km; Vmax remains unchanged
• D. It competes with substrate and reduces enzyme efficiency but Vmax decreases

Answer: (C)

In competitive inhibition, the inhibitor mimics the substrate and binds to the enzyme’s active site, blocking substrate binding. Because both substrate and inhibitor vie for the same site, higher substrate concentrations can outcompete the inhibitor, allowing the reaction to reach its maximum rate. This keeps Vmax the same, since once enough substrate is present, the enzyme can achieve its maximal speed. However, the apparent affinity for substrate drops, so Km appears higher because more substrate is needed to reach half-maximal velocity. The description that best fits this is the one stating that the inhibitor binds to the active site, increases apparent Km, and leaves Vmax unchanged. The other scenarios describe different modes of inhibition (such as binding at an allosteric site with reduced Vmax, irreversible binding, or decreases in Vmax while competing with substrate), which do not match true competitive inhibition.

In competitive inhibition, the inhibitor mimics the substrate and binds to the enzyme’s active site, blocking substrate binding. Because both substrate and inhibitor vie for the same site, higher substrate concentrations can outcompete the inhibitor, allowing the reaction to reach its maximum rate. This keeps Vmax the same, since once enough substrate is present, the enzyme can achieve its maximal speed. However, the apparent affinity for substrate drops, so Km appears higher because more substrate is needed to reach half-maximal velocity. The description that best fits this is the one stating that the inhibitor binds to the active site, increases apparent Km, and leaves Vmax unchanged. The other scenarios describe different modes of inhibition (such as binding at an allosteric site with reduced Vmax, irreversible binding, or decreases in Vmax while competing with substrate), which do not match true competitive inhibition.