apóenzyme

An apoenzyme is the protein component of an enzyme that requires a cofactor for its biological activity. When a cofactor binds to an apoenzyme, it forms a complete, active enzyme called a holoenzyme. Apoenzymes are typically inactive on their own and cannot catalyze their specific biochemical reactions. The term "apo" comes from the Greek word for "away" or "from," indicating that the active part of the enzyme has been removed.

Cofactors can be either inorganic ions, such as magnesium or zinc, or organic molecules known as coenzymes. Coenzymes are often derived from vitamins. The binding of the cofactor to the apoenzyme is usually specific and can be reversible or irreversible. This interaction often involves the formation of a specific three-dimensional structure within the apoenzyme that creates the active site where the substrate binds and the reaction occurs. The role of the apoenzyme is to provide the catalytic machinery and the binding specificity, while the cofactor often participates directly in the chemical reaction or helps to stabilize the transition state. Understanding the distinction between apoenzymes and holoenzymes is crucial for comprehending enzyme function and regulation in biological systems.