Enzyme inhibition

The inhibition of enzymes is an important process in biochemistry to influence the effectiveness of enzymes. Inhibitors (enzymes, proteins, or chemicals) usually bind to enzymes, thus limiting their catalytic function. This can happen in various ways.

Irreversible Inhibition

In such cases, the enzyme is inactivated by an irreversible interaction (usually a covalent interaction) with the inhibitor. These substances bind to the active site of the enzyme, thus preventing the formation of the enzyme-substrate complex. This includes, among others, heavy metal ions, which inactivate the enzyme when they bind to a thiol group in the active site.

Reversible Inhibition

In reversible inhibition, the inhibitors only temporarily hinder the enzyme and can also be released again. There are different types of inhibition here.

Competitive Inhibition

The inhibitor binds directly to the active site of the free enzyme, preventing it from binding to the substrate. However, only a part of the enzyme binds the inhibitor, while the rest binds the substrate and forms a product. The binding of the inhibitor slows down the reaction at a constant substrate concentration. However, the maximum reaction rate is not affected, but more substrate is needed to reach it.

Uncompetitive Inhibition

In this case, the inhibitor does not bind to the enzyme directly, but to the enzyme-substrate complex. In this case too, the reaction is slowed down and the maximum reaction rate as well as the K_M value are also reduced. However, the reduction in the K_M value here does not mean an increased affinity for the substrate, but a shift in the reaction equilibrium.

Non-competitive Inhibition

In this case, the order in which the substrate and inhibitor bind to the enzyme is not fixed. This significantly reduces the reaction rate and the maximum reaction rate.

Now we have learned how enzymes work and how their activity can be influenced. But where do we actually encounter these enzymes in everyday life?