What is the inhibition constant (KI) in the context of enzyme-inhibitor interactions?

• A. The inhibition constant is the rate at which an enzyme catalyzes a reaction.
• B. The inhibition constant is the concentration of inhibitor required to completely stop the enzyme activity.
• C. The inhibition constant is a measure of the binding affinity between an enzyme and an inhibitor.
• D. The inhibition constant is the concentration of substrate required to reach half of the maximum reaction velocity.

Answer: (C)