Which statement most accurately explains how allosteric regulation can change an enzyme's catalytic activity?

Out of the following given choices;

In allosteric inhibition, a regulatory molecule binds to a location other than the active site, resulting in a change in enzyme shape that allows the active site to bind substrate.

In allosteric activation, a regulatory molecule binds to a location other than the active site, resulting in a change in enzyme shape that allows the active site to bind substrate.

In allosteric inhibition, a regulatory molecule binds to the active site, blocking substrate binding.

In allosteric activation, a regulatory molecule binds to the active site, allowing substrate binding.

The answer is B. When an effector molecule binds to an allosteric site, the enzyme changes conformation causing the enzyme to have a high affinity for its ligand at the active site. A good example to explain allosteric regulation is hemoglobin (which is not an enzyme though). The subunits of the hemoglobin have allosteric effects on each other. When oxygen binds to one subunit, its conformation change causing the subunit to bind to the allosteric site of adjacent subunits. This subsequently causes the other subunits to have more affinity for oxygen in their oxygen-binding active sites.  

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