enzymeinhibitor

An enzyme inhibitor is a molecule that decreases the activity of an enzyme by interfering with its catalytic function. Inhibitors can act reversibly or irreversibly and may interact with the active site, the enzyme’s substrate binding site, or an allosteric region that modulates activity.

Reversible inhibitors fall into several classes. Competitive inhibitors resemble the substrate and compete for binding at the active site, reducing the apparent affinity for substrate. Noncompetitive inhibitors bind to a separate site and reduce catalytic efficiency without directly preventing substrate binding. Uncompetitive inhibitors bind only to the enzyme–substrate complex, and mixed inhibition displays features of both competitive and noncompetitive behavior.

Irreversible inhibitors form covalent bonds or otherwise permanently modify the enzyme, often causing lasting inactivation. Classic examples include aspirin, which acetylates cyclooxygenase; penicillin, which inhibits bacterial transpeptidase; and organophosphates, which pin down acetylcholinesterase.

Many organisms produce endogenous inhibitors to regulate metabolism and protect tissues. Serpins inhibit serine proteases, while tissue inhibitors of metalloproteinases (TIMPs) block metalloproteinases, helping control proteolytic activity.

In enzyme kinetics, inhibition is described by constants such as the inhibition constant Ki and, for some assays, the IC50 value that indicates the concentration required to reduce activity by 50%. These metrics are central to drug discovery and to understanding metabolic control.

In medicine, inhibitors are used therapeutically to modulate disease processes, including ACE inhibitors for hypertension, COX inhibitors for pain and inflammation, and protease inhibitors for viral infections. In industry, enzyme inhibitors also help regulate biocatalytic processes and improve product yields.