Which type of enzyme inhibition is demonstrated by competitive binding to the active site?

• A. Competitive Inhibition
• B. Noncompetitive Inhibition
• C. Uncompetitive Inhibition
• D. Mixed Inhibition

Answer: (A)

Competitive inhibition happens when an inhibitor binds directly to the enzyme’s active site, blocking substrate from binding. Because the inhibitor and substrate compete for the same site, the reaction rate at a given substrate concentration drops, but increasing substrate concentration can outcompete the inhibitor and restore the rate. The maximum rate (Vmax) remains unchanged, since the enzyme can still reach it if enough substrate is present, while the apparent affinity for substrate increases (Km goes up) because more substrate is needed to reach half-max velocity. This pattern—binding at the active site and competing with the substrate—distinguishes it from other types of inhibition that alter Vmax or act on the enzyme–substrate complex rather than the active site.