What is a competitive inhibitor?

A competitive inhibitor is a molecule that specifically binds to an enzyme's active site, the region where substrates normally bind to facilitate a chemical reaction. By occupying this site, the competitive inhibitor effectively blocks substrates from accessing the active site, which decreases the rate of the reaction catalyzed by the enzyme. This competition for the active site means that the presence of the inhibitor can be overcome by increasing substrate concentration, as more substrates can outcompete the inhibitor for binding to the active site.

In contrast, other options describe different concepts. Options that refer to enhancing enzyme action or non-protein components do not define how a competitive inhibitor operates since these do not involve blocking the active site. Similarly, describing a product of an enzymatic reaction does not relate to the inhibition process; products are a result of enzyme action rather than a means of inhibiting it. Thus, the correct definition accurately describes the mechanism by which competitive inhibitors function in enzyme kinetics.