What distinguishes competitive inhibition from non-competitive inhibition?

• A. Competitive inhibition increases substrate affinity
• B. Non-competitive inhibition occurs at the active site
• C. Competitive inhibition involves the active site, while non-competitive involves an allosteric site
• D. Non-competitive inhibition increases enzyme activity

Answer: (C)

Competitive inhibition and non-competitive inhibition are two mechanisms by which enzyme activity can be affected by the presence of inhibitors. The distinguishing factor between them lies in their interaction with the enzyme.

In competitive inhibition, the inhibitor competes with the substrate for binding at the enzyme's active site. This means that both the substrate and the inhibitor cannot bind to the active site simultaneously. As a result, increasing the concentration of the substrate can overcome the inhibition, as it increases the likelihood that the substrate will bind to the active site instead of the inhibitor.

On the other hand, non-competitive inhibition occurs when the inhibitor binds to a site other than the active site, often referred to as an allosteric site. This binding changes the enzyme's conformation, which can reduce the enzyme's overall activity regardless of the substrate concentration. In contrast to competitive inhibition, increasing the substrate concentration does not overcome non-competitive inhibition because the presence of the inhibitor still affects the enzyme's ability to catalyze the reaction effectively.

Thus, the correct answer accurately captures the essence of these two types of inhibition by stating that competitive inhibition involves the active site, while non-competitive inhibition involves binding at an allosteric site, leading to distinct implications for enzyme kinetics and substrate binding.