Enzyme inhibitors

Enzyme inhibitors (lat. inhibere 'stop') are endogenous or exogenous substances that bind to specific enzymes and suppress or slow down their metabolic reactions. In most cases, the enzyme itself is altered by binding in such a way that it becomes functionless. Enzyme inhibitors can dock competitively or non-competitively at different sites of an enzyme (e.g. active centre, allosteric centre) and inhibit these reversibly or irreversibly (see belowenzyme inhibition). Many inhibitors are analogues of the natural substrate.

A large number of drugs belong to the group of enzyme inhibitors. Examples of medicinal enzyme inhibitors are

• ACE inhibitors: ACE inhibitors block the angiotensin converting enzyme. This enzyme catalyzes the formation of angiotensin II from angiotensin I. Thus, the effects of angiotensin II are cancelled. The blood pressure is lowered.
• Non-steroidal anti-inflammatory drugs (NSAID): This group of substances reversibly inhibits cyclooxygenases and thus the prostaglandin synthesis.
• Cholinesterase inhibitors (indirect parasympathomimetics such as physostigmine inhibit the enzymatic degradation of acetylcholine by cholinesterases)
• Reverse transcriptase inhibitors (RTI) such as ziduvidin, which inhibit the transcription of viral RNA into DNA during HIV infection.
• Protease inhibitors such as indinavir, which inhibit the catalytic function of HIV protease. This leads to HIV particles with immature morphology
• Xanthine oxidase inhibitors (gout therapeutics such as allopurinol which prevent the conversion of hypoxanthine to uric acid by competitively inhibiting xanthine oxidase)
• Proton pump inhibitors (substances such as omaprazole which selectively inhibit the H+/K+-ATPase in the lining cells of the stomach mucosa (proton pump).