What is allosteric regulation and how does it affect enzyme activity?

• A. Binding at active site to block substrate
• B. Binding of substrate to active site to increase rate
• C. Binding of molecule at a site other than active site modulates activity by changing enzyme shape
• D. Irreversibly destroying enzyme

Answer: (C)

Allosteric regulation involves a molecule binding to an enzyme at a site away from the active site, called the allosteric site. This binding induces a change in the enzyme’s shape, which can alter how well the active site binds substrate or how effectively the enzyme catalyzes the reaction. The result can be an increase or decrease in activity, depending on the effector.

This description matches the idea of regulation through a regulatory site changing the enzyme’s conformation. For example, a metabolite or product can bind allosterically to slow down or speed up an enzyme in response to cellular conditions.

The other scenarios don’t fit allosteric regulation because they involve interactions at the active site itself or non-reversible damage: blocking the active site is competitive inhibition at the active site; substrate binding at the active site to raise rate is just normal catalysis by substrate; and irreversibly destroying the enzyme is not regulation at all but permanent inactivation.