kofactor

A cofactor is a non-protein chemical compound or metallic ion that is required for a protein's biological activity. Cofactors can be permanently bound to the enzyme's active site or may bind reversibly. They are often essential for the enzyme to catalyze its specific reaction. Without the proper cofactor, an enzyme may lose its catalytic activity.

Cofactors are broadly categorized into two types: inorganic ions and organic molecules. Inorganic cofactors are typically metal ions such as magnesium, zinc, or iron. These ions can play a variety of roles, including stabilizing the enzyme structure, assisting in substrate binding, or participating directly in the catalytic mechanism by donating or accepting electrons.

Organic cofactors are called coenzymes. Many coenzymes are derived from vitamins. For example, NAD+ (nicotinamide adenine dinucleotide) and FAD (flavin adenine dinucleotide) are important coenzymes involved in redox reactions, and they are derived from niacin (vitamin B3) and riboflavin (vitamin B2), respectively. Coenzymes often act as transient carriers of specific functional groups, atoms, or electrons during a reaction. They bind to the enzyme, facilitate the chemical transformation, and then are released, often in a modified form, to participate in further reactions. The molecule upon which a cofactor acts is called a substrate.