Enzyme Inhibitors and Reaction Kinetics

Competitive Inhibition

A competitive inhibitor is a molecule that binds directly to the active site of an enzyme, preventing the binding of the substrate. When competitive inhibitors are present, a higher concentration of substrate is required to achieve the same rate of reaction and reach maximum velocity ($V_{\text{max}}$). The effects of a competitive inhibitor can be overcome by increasing the substrate concentration.

Noncompetitive and Allosteric Regulation

A noncompetitive inhibitor is a molecule that binds to an enzyme at an allosteric site, which is separate from the active site. This binding alters the active site's shape, preventing the substrate from binding, reducing binding ease, or preventing catalysis even if bound. All noncompetitive inhibitors reduce the total number of usable enzymes and lower $V_{\text{max}}$. Noncompetitive inhibition is a form of allosteric regulation, where molecules binding to an allosteric site can also potentially increase enzyme activity.

Irreversible Inhibition

An irreversible inhibitor is a molecule that covalently bonds to the active site of an enzyme, permanently deactivating it. Cells do not typically use irreversible inhibitors for regulation due to the permanent loss of functional enzymes. An example of an irreversible inhibitor is diisopropyl phosphorofluoridate (DIFP), a nerve gas that disables essential enzymes in neurons.