A reaction inhibitor is a
substance
Substance may refer to:
* Matter, anything that has mass and takes up space
Chemistry
* Chemical substance, a material with a definite chemical composition
* Drug, a chemical agent affecting an organism
Arts, entertainment, and media Music
* ' ...
that decreases the rate of, or prevents, a
chemical reaction
A chemical reaction is a process that leads to the chemistry, chemical transformation of one set of chemical substances to another. When chemical reactions occur, the atoms are rearranged and the reaction is accompanied by an Gibbs free energy, ...
.
A
catalyst
Catalysis () is the increase in rate of a chemical reaction due to an added substance known as a catalyst (). Catalysts are not consumed by the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recycles quick ...
or an
Enzyme activator
Enzyme activators are molecules that bind to enzymes and increase their activity. They are the opposite of enzyme inhibitors. These molecules are often involved in the allosteric regulation of enzymes in the control of metabolism
Metaboli ...
, in contrast, is a substance that increases the rate of a chemical reaction.
Examples
* Added
acetanilide slows the decomposition of drug-store
hydrogen peroxide
Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscosity, viscous than Properties of water, water. It is used as an oxidizer, bleaching agent, and antiseptic, usua ...
solution, inhibiting the reaction
2 → 2 + , which is catalyzed by heat, light, and impurities.
[The decomposition of hydrogen peroxide]
Inhibition of a catalyst
An inhibitor can reduce the effectiveness of a
catalyst
Catalysis () is the increase in rate of a chemical reaction due to an added substance known as a catalyst (). Catalysts are not consumed by the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recycles quick ...
in a catalysed reaction (either a non-biological catalyst or an
enzyme
An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...
). E.g., if a compound is so similar to (one of) the reactants that it can bind to the active site of a catalyst but does not undergo a catalytic reaction then that catalyst molecule cannot perform its job because the active site is occupied. When the inhibitor is released, the catalyst is again available for reaction.
Inhibition and catalyst poisoning
Inhibition should be distinguished from catalyst poisoning. An inhibitor only hinders the working of a catalyst without changing it, whilst in catalyst poisoning the catalyst undergoes a chemical reaction that is irreversible in the environment in question (the active catalyst may only be regained by a separate process).
Potency
Index inhibitors or simplified as inhibitor predictably inhibit metabolism via a given
pathway and are commonly used in prospective clinical
drug-drug interaction studies.
Inhibitors of
CYP can be classified by their
potency, such as:
*Strong inhibitor being one that causes at least a 5-fold increase in the plasma
AUC values, or more than 80% decrease in
clearance of
substrates ( Over 1.8 times slower than usual clearance rate.) .
*Moderate inhibitor being one that causes at least a 2-fold increase in the plasma AUC values, or 50-80% decrease in clearance of substrates ( At least 1.5-1.8 times slower than usual clearance speed.) .
*Weak inhibitor being one that causes at least a 1.25-fold but less than 2-fold increase in the plasma AUC values, or 20-50% decrease in clearance of substrates ( At least 1.2-1.5 times slower than usual clearance rate.) .
See also
*
Enzyme inhibition
An enzyme inhibitor is a molecule that binds to an enzyme and blocks its Enzyme activity, activity. Enzymes are proteins that speed up chemical reactions necessary for life, in which Substrate (biochemistry), substrate molecules are converted ...
*
Catalyst poisoning Catalyst poisoning is the partial or total deactivation of a catalyst by a chemical compound. Poisoning refers specifically to chemical deactivation, rather than other mechanisms of catalyst degradation such as thermal decomposition or physical da ...
References
Catalysis
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