Noncompetitive inhibition

Noncompetitive inhibition is a type of enzyme inhibition where the inhibitor reduces the activity of the enzyme and binds equally well to the enzyme whether it has already bound the substrate or not.

Mechanism

In noncompetitive inhibition, the affinity of the enzyme for the substrate is equivalent in the presence or absence of the inhibitor. This is because the inhibitor has an equal affinity for the enzyme and the enzyme-substrate complex. The inhibitor binds to an allosteric site and prevents the enzyme from forming a product by causing a conformational change in its active site.

Types

Noncompetitive inhibition can be reversible or irreversible.

• Reversible noncompetitive inhibition occurs when the inhibitor forms weak interactions with the enzyme or enzyme-substrate complex and can easily be removed.
• Irreversible noncompetitive inhibition occurs when the inhibitor forms strong covalent bonds with the enzyme, permanently inactivating it.

Effects

Noncompetitive inhibition has two main effects on enzyme kinetics:

• It decreases the maximum rate of reaction (Vmax), as there are fewer enzyme molecules available for catalysis.
• It does not change the Michaelis constant (Km), as the affinity of the enzyme for the substrate remains the same.

Examples

Examples of noncompetitive inhibitors include metabolic poisons such as cyanide and some drugs such as aspirin and statins.

See also

• Competitive inhibition
• Uncompetitive inhibition
• Mixed inhibition

References

Noncompetitive inhibition Resources
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