Andy Sotiriou/Photodisc/Getty Images

Enzymes accelerate specific chemical reactions, but many require a cofactor—a non‑protein ion or molecule—to perform their function. When a cofactor is absent, the enzyme loses its catalytic ability, rendering the reaction ineffective.

Function

A cofactor is an essential non‑protein component that enables an enzyme to catalyze its reaction. Removing the cofactor halts the enzyme’s activity. For instance, carbonic anhydrase in human blood converts water and carbon dioxide into carbonic acid; it requires a zinc ion to bind water and facilitate the reaction. Without zinc, carbonic anhydrase becomes inactive.

Types

Cofactors come in two main varieties:

• Metal ions such as iron, magnesium, and zinc.
• Small organic molecules like vitamin B12, which often act as coenzymes.

Many vitamins serve as enzyme cofactors or precursors. Some cofactors are tightly bound and become integral parts of the enzyme, known as prosthetic groups, while others bind loosely.

Mechanism

The role of a cofactor depends on the enzyme’s catalytic mechanism. In carbonic anhydrase, the zinc ion sits in the active‑site cleft and attracts a water molecule. Its positive charge stabilizes the formation of a hydroxide ion, which then attacks carbon dioxide to form carbonic acid. By enabling the loss of a hydrogen ion from water, zinc directly drives the reaction.

Applications

Intentionally removing a cofactor is a common strategy to inhibit unwanted enzymatic activity. In molecular biology, EDTA chelates magnesium ions, rendering DNases inactive and protecting extracted DNA. Similarly, many antibiotics target bacterial enzymes by binding or displacing essential metal cofactors.