Explain allosteric inhibition with an example.

ANSWER: Consider as an illustration the following pathway, where A is the precursor for formation of an end product, F, in a sequence of five enzyme-catalyzed reactions:

In this scheme, F symbolizes an essential metabolite, such as an amino acid or a nucleotide. In such systems, F, the essential end product, inhibits enzyme 1, the first step in the pathway. Therefore, when sufficient F is synthesized, it blocks further synthesis of itself. This phenomenon is called feedback inhibition or feedback regulation. The feedback inhibitor F bears little structural similarity to A, the substrate for the regulatory enzyme. F apparently acts at a binding site distinct from the substrate-binding site. The term allosteric is apt, because F is sterically dissimilar and, moreover, acts at a site other than the site for S. Its effect is called allosteric inhibition.