inhibiitor

An inhibitor is a substance that decreases or blocks the activity of another molecule, most often an enzyme, receptor, or signaling protein. In biochemistry and pharmacology, inhibitors regulate metabolic processes, study mechanisms, and treat disease by interfering with specific biochemical targets.

Enzyme inhibitors can be reversible or irreversible. Reversible inhibitors may be competitive, noncompetitive, uncompetitive, or mixed. Competitive inhibitors resemble the substrate and compete for the active site, reducing the effective concentration of enzyme-substrate complex. Noncompetitive inhibitors bind to a different site (an allosteric site) and change the enzyme's shape, reducing activity without directly blocking substrate binding. Uncompetitive inhibitors bind only to the enzyme-substrate complex. Irreversible inhibitors form covalent bonds with the enzyme, permanently inactivating it.

In medicine, inhibitors underpin many therapies. Penicillin and related beta-lactam antibiotics inhibit bacterial transpeptidases, blocking cell wall synthesis. Aspirin irreversibly inhibits cyclooxygenases, reducing prostaglandin production. ACE inhibitors lower blood pressure by blocking angiotensin-converting enzyme. HIV protease inhibitors block viral maturation. Tyrosine kinase inhibitors target growth signaling in cancer. In research, inhibitors serve as tools to dissect pathways and as diagnostic or therapeutic agents.

Outside biology, inhibitors include chemical agents that slow or prevent polymerization, metal corrosion inhibitors, and enzyme inhibitors used to protect foods from spoilage. Potency and selectivity are quantified by parameters such as IC50 and Ki. The standard term in English is inhibitor; “inhibiitor” is a nonstandard or misspelled variant.