cofacteur

A cofactor is a non-protein chemical compound or metallic ion that is required for a protein's biological activity. Proteins, especially enzymes, often need cofactors to function properly. Cofactors can be broadly categorized into two main types: inorganic ions and organic molecules.

Inorganic cofactors are typically metal ions. Examples include iron (Fe2+ or Fe3+), magnesium (Mg2+), zinc (Zn2+), and copper (Cu2+). These ions often play a role in the catalytic activity of enzymes, either by directly participating in the reaction mechanism or by helping to position the substrate. For instance, magnesium ions are commonly found in enzymes that involve ATP hydrolysis.

Organic cofactors are called coenzymes. Many coenzymes are derived from vitamins. Examples include NAD+ (nicotinamide adenine dinucleotide), FAD (flavin adenine dinucleotide), and coenzyme A. These coenzymes often act as carriers of specific chemical groups, such as electrons, hydrogen atoms, or acyl groups, during biochemical reactions.

When a cofactor is tightly bound to an enzyme, it is called a prosthetic group. If the cofactor is loosely bound and can dissociate from the enzyme, it is called a cosubstrate. The combination of an enzyme and its cofactor is called a holoenzyme, while the enzyme without its cofactor is called an apoenzyme. The apoenzyme is generally inactive, and the holoenzyme is the active form. Cofactors are essential for the proper functioning of many biological processes.