Noncompetitive

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 or not it has already bound the substrate.

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 on the enzyme to inhibit enzyme-substrate interaction. This changes the shape of the enzyme and thus the active site, so that the substrate can no longer bind to it.

Types

Noncompetitive inhibition can be reversible or irreversible.

• Reversible noncompetitive inhibition involves the inhibitor binding to the enzyme, but it can be removed by increasing substrate concentration.
• Irreversible noncompetitive inhibition involves the inhibitor binding permanently to the enzyme, rendering it inactive.

Examples

Examples of noncompetitive inhibitors include metabolic poisons such as cyanide and some pesticides. These substances can bind to enzymes in the mitochondria of cells, preventing cellular respiration and leading to cell death.

See also

• Enzyme kinetics
• Competitive inhibition
• Uncompetitive inhibitor
• Mixed inhibition

References

Noncompetitive Resources
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