Final answer:
Allosteric regulation represents a rapid and reversible mechanism to alter the activity of an enzyme, often involving non-covalent binding at a site other than the active site which results in conformational changes that affect enzyme activity.
Step-by-step explanation:
The rapid and reversible mechanism to alter the activity of an enzyme is represented by allosteric regulation. Allosteric enzymes have a second binding site, known as the allosteric site, in addition to the active site where substrates bind. When an allosteric activator or inhibitor binds to this site, it induces a conformational change in the enzyme that can either increase or decrease its activity. This type of regulation is rapid and easily reversible, as the bond between the enzyme and the allosteric effector is non-covalent and can dissociate readily. In contrast, covalent modifications are typically slower processes and not as rapidly reversible. Irreversible inhibition, as the name suggests, is not reversible, and competitive inhibition, while reversible, does not act as rapidly because it requires the competitive inhibitor to be outcompeted by the substrate for its effect to be reversed.
Competitive inhibitors and noncompetitive inhibitors differ in their binding sites and effects on enzyme activity. Competitive inhibitors bind to the active site of an enzyme and compete with the substrate for binding. Noncompetitive inhibitors, on the other hand, bind to an allosteric site, causing a change in enzyme conformation that affects its activity. It's important to note that feedback inhibition is a form of allosteric regulation which involves the end-product of a metabolic pathway acting as a noncompetitive inhibitor to an enzyme involved earlier in the pathway, thus regulating the pathway's overall output.