Enzyme inhibitor

An enzyme inhibitor is a molecule that binds to an enzyme and decreases its activity. By binding to enzymes' active sites, inhibitors reduce the compatibility of substrate and enzyme and this leads to the inhibition of Enzyme-Substrate complexes' formation, preventing the enzyme from catalyzing its reaction.

Types of Enzyme Inhibitors

Enzyme inhibitors are classified into two main types: Reversible inhibitors and Irreversible inhibitors.

Reversible Inhibitors

Reversible inhibitors bind to enzymes with non-covalent interactions such as hydrogen bonds, hydrophobic interactions, and ionic bonds. Multiple weak bonds between the inhibitor and the active site combine to produce strong and specific binding. In contrast to substrates and irreversible inhibitors, reversible inhibitors generally do not undergo chemical reactions when bound to the enzyme and can be easily removed by dilution or dialysis.

There are three kinds of reversible inhibitors: Competitive inhibitors, Noncompetitive inhibitors, and Uncompetitive inhibitors.

Competitive Inhibitors

Competitive inhibitors bind to the active site and prevent the substrate from binding there. The inhibition can be overcome by increasing the concentrations of substrate, to out-compete the inhibitor. Competitive inhibitors are often similar in structure to the real substrate.

Noncompetitive Inhibitors

Noncompetitive inhibitors bind to an enzyme at a site distinct from the active site. The enzyme-inhibitor complex can still bind substrate in the active site, forming an ESI complex, but the ESI complex does not form product.

Uncompetitive Inhibitors

Uncompetitive inhibitors bind to the enzyme-substrate complex, preventing it from releasing products. These inhibitors modify the enzyme's active site, making it less receptive to the substrate.

Irreversible Inhibitors

Irreversible inhibitors usually form covalent bonds with enzymes, irreversibly inactivating them. The inhibition cannot be reversed by an excess of substrate. Irreversible inhibitors often contain reactive functional groups such as nitrogen mustards, aldehydes, haloalkanes, alkenes, Michael acceptors, phenyl sulphonates, or fluorophosphonates.

Medical Applications

Enzyme inhibitors are used as drugs to treat diseases. They can be used to decrease abnormal enzyme activity in diseases such as cancer, HIV, and hypertension. Some of the most common enzyme inhibitors include ACE inhibitors, Protease inhibitors, and Chemotherapy drugs.

See Also

• Enzyme
• Reversible inhibitors
• Irreversible inhibitors
• Competitive inhibitors
• Noncompetitive inhibitors
• Uncompetitive inhibitors
• ACE inhibitors
• Protein Kinase Inhibitors
• Chemotherapy

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