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An inhibitor can reduce the effectiveness of a catalyst in a catalysed reaction (either a non-biological catalyst or an enzyme).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.
The term 'inhibitor' is often used in a general sense to describe any compound used to prevent unwanted polymerisation, however these compounds are often divided into 'retarders' and 'true inhibitors'. A true inhibitor has a well defined induction period during which no noticeable polymerisation takes place. They are consumed during this period ...
An illustrative example is the effect of catalysts to speed the decomposition of hydrogen peroxide into water and oxygen: . 2 H 2 O 2 → 2 H 2 O + O 2. This reaction proceeds because the reaction products are more stable than the starting compound, but this decomposition is so slow that hydrogen peroxide solutions are commercially available.
This type of inhibition reduces the maximum rate of a chemical reaction without changing the apparent binding affinity of the catalyst for the substrate (K m app – see Michaelis-Menten kinetics). When a non-competitive inhibitor is added the Vmax is changed, while the Km remains unchanged.
In contrast to irreversible inhibitors, reversible inhibitors generally do not undergo chemical reactions when bound to the enzyme and can be easily removed by dilution or dialysis. A special case is covalent reversible inhibitors that form a chemical bond with the enzyme, but the bond can be cleaved so the inhibition is fully reversible. [13]
Once the inhibitor is bound to the enzyme, the slope will be affected, as the K m either increases or decreases from the original K m of the reaction. [4] [5] [6] Most competitive inhibitors function by binding reversibly to the active site of the enzyme. [1] As a result, many sources state that this is the defining feature of competitive ...
Catalysts can only speed up the reaction – chemicals that slow down the reaction are called inhibitors. [ 41 ] [ 42 ] Substances that increase the activity of catalysts are called promoters, and substances that deactivate catalysts are called catalytic poisons.
The reaction catalysed by an enzyme uses exactly the same reactants and produces exactly the same products as the uncatalysed reaction. Like other catalysts, enzymes do not alter the position of equilibrium between substrates and products. [1] However, unlike uncatalysed chemical reactions, enzyme-catalysed reactions display saturation kinetics.