In the presence of a competitive inhibitor, adding substrate will?

• A. Reverses the inhibition
• B. Increases Km
• C. Increases Vmax
• D. No effect

Answer: (A)

In competitive inhibition, the inhibitor and the substrate compete for the same active site on the enzyme. The inhibitor reduces the enzyme’s apparent affinity for the substrate, so at a given substrate level the reaction goes more slowly. But this effect can be overcome by adding more substrate. When substrate concentration is increased, it is more likely to bind the enzyme than the inhibitor, allowing the enzyme to reach higher rates and approach the uninhibited maximum velocity. So, adding substrate effectively reverses or surmounts the inhibition.