The other binding site is called the allosteric. The molecule that binds to the allosteric site is an inhibitor because it causes a change in the 3-dimensional structure of the enzyme that prevents the substrate from binding to the active site. Irreversible inhibition of enzymes also occurs, due to the presence of a poison. For example, penicillin cause the death of bacteria due to irreversible inhibition of an enzyme needed to form the bacterial cell wall. The activity of almost every enzyme is a cell is regulated by feedback inhibition.
Feedback inhibition is an example of common biological control mechanism called negative feedback.
Just as high temperature will cause furnace to shut off, in a similar manner the product of an enzyme can inhibit a enzyme reaction. In this way the concentration of the product is always controlled within a certain range. Activation of an allosteric enzyme by an activator is another form of feedback inhibition. Combination of the activator and the allosteric site cause a conformational change in the active site permitting substrate binding and the reaction will be catalyzed. Most enzymatic pathways are also regulated by feedback inhibition, but in these cases the end product of the pathway binds at an allosteric site on the first enzyme of the pathway.