Enzyme inhibitors are molecules that interfere with catalysis, slowing or halting enzymatic reactions. There are two broad classes of enzyme inhibitors: reversible and irreversible.
Reversible inhibition: Common type of Reversible inhibition is called competitive. A competitive inhibition competes with the substrate for the active site of an enzyme. While the inhibitor (I) occupies the active site it prevents binding of the substrate to the enzyme. In competitive inhibition the Vmax remains the same but the Km of the reaction increase.
E.g. ethanol competes effectively with methanol as an alternative substrate for the enzyme alcohol dehydrogenase.
Two other types of reversible inhibition are uncompetitive and mixed.
An uncompetitive inhibitor binds at a site distinct from the substrate active site end and, unlike a competitive inhibitor, binds only to the enzyme-substrate [ES] complex. An uncompetitive inhibitor lowers the measured Vmax and the Km decreases.
A mixed inhibitor also binds at a site distinct from the substrate active site, but it binds to either E or [ES]. It usually affects both the Vmax and Km.
Irreversible inhibition: the irreversible inhibitors bind covalently with or destroy a functional group on an enzyme that is essential for the enzymes’s activity, or form a particularly stable noncovalent association.
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