Enzyme inhibition

Reversible or non-reversible inhibition of the activity of an enzyme through competitive or non-competitive inhibition or through an excess supply of substrate (substrate inhibition).

A distinction is made between the:

• reversible and the
• non-reversible inhibition

between the:

• competitive, and the
• non-competitive (allosteric)

Inhibition of enzymes.

Competitive inhibition: Enzymes function according to the lock-and-key principle. Only the appropriate substrate can bind to the active centre and be processed. Substances that are structurally similar to a substrate can also bind to the active site of the enzyme. They thus block the binding and processing of the "actual" substrate. Inhibitor and substrate therefore compete for the same binding site.

Non-competitive inhibition (also allosteric inhibition (from allos greek others, stereos= solid). Here, certain low-molecular compounds do not occupy the active centre of the enzyme, but other "docking sites" outside the actual binding centre, so-called allosteric centres. The binding of an inhibitor to these docking sites leads to a change in the spatial shape of the enzyme (conformational change). This inhibits the active centre and thus the enzyme in its function (the opposite can also occur).

Irreversible inhibition: In irreversible inhibition, an inhibitor (e.g. an enzyme poison) enters into a permanent bond with an enzyme, which permanently renders the enzyme inoperable. Many enzymes containing heavy metals (e.g. those of the iron-containing respiratory chain) are irreversibly inhibited by cyanides.

The inhibition and activation of enzymes plays an important role in the metabolism of drugs, which influences half-lives, increases or decreases the effect, and increases the ADR (allergic reactions, toxicities). Numerous drugs (enzyme inhibitors e.g. cholinesterase inhibitors, protease inhibitors, proton pump inhibitors) are based on the principle of enzyme inhibition.

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