Inhibitor

An inhibitor is a substance that decreases the rate of a chemical reaction or the activity of a biological system. In chemistry and biochemistry, inhibitors interact with reactants, catalysts, or enzymes to slow or prevent processes. In pharmacology, many drugs act as inhibitors of specific enzymes, receptors, or transporters to modulate physiological pathways.

Enzyme inhibitors are commonly classified by mechanism. Competitive inhibitors bind to the active site and block substrate access, reducing the reaction rate as substrate concentration increases. Noncompetitive inhibitors bind to an allosteric site and decrease enzyme activity regardless of substrate levels. Uncompetitive inhibitors bind only to the enzyme–substrate complex. Inhibitors can be reversible, forming non-covalent interactions, or irreversible, often by covalent modification of the target.

In pharmacology and medicine, inhibitors serve as therapeutic agents. For example, aspirin irreversibly acetylates and inhibits cyclooxygenase, reducing prostaglandin synthesis. ACE inhibitors block angiotensin-converting enzyme to lower blood pressure. Statins inhibit HMG-CoA reductase to reduce cholesterol synthesis, and viral protease inhibitors block maturation of certain viruses. In research, selective inhibitors help dissect enzyme function and regulatory pathways, while in industry, inhibitors prevent unwanted reactions or degradation.

Assessment of inhibition uses parameters such as IC50 and Ki. IC50 is the inhibitor concentration required to achieve 50% inhibition under specific conditions and can vary with substrate concentration; Ki is a constant reflecting binding affinity. Kinetic analyses, often using Michaelis–Menten or Lineweaver–Burk plots, help determine the mode and strength of inhibition.

Overall, inhibitors are central tools in science and medicine, enabling control and study of chemical and biological processes, while also carrying considerations of specificity and safety.