How do competitive and non-competitive inhibitors differ in their mechanism of action?

• A. Competitive inhibitors bind to the active site, while non-competitive inhibitors do not
• B. Non-competitive inhibitors increase activity at the active site
• C. Both types inhibit enzyme action by binding to the same site
• D. Non-competitive inhibitors can be reversed by increasing substrate concentration

Answer: (A)

The distinction between competitive and non-competitive inhibitors primarily lies in their interaction with the enzyme and where they bind. Competitive inhibitors specifically bind to the active site of the enzyme, the region where the substrate normally binds. By occupying this site, they compete with the substrate for access, thereby effectively reducing the rate of the reaction when the substrate is present. This effect can be overcome by increasing substrate concentration, as higher levels of substrate increase the likelihood of binding the active site over the inhibitor.

Non-competitive inhibitors, on the other hand, bind to a different site on the enzyme, which does not directly interfere with the substrate binding at the active site. Instead, their binding changes the enzyme's shape or function, thus decreasing the maximum reaction rate regardless of substrate concentration. This means that even with an excess of substrate, the presence of a non-competitive inhibitor will hinder enzyme activity.

This understanding clarifies why the correct answer highlights that competitive inhibitors bind to the active site while non-competitive inhibitors do not interact with that site.