holozymes

Holozymes are a class of enzymes that, in addition to their protein component, require a non-protein moiety, known as a cofactor, for their catalytic activity. This cofactor is tightly bound to the enzyme and is essential for the enzyme to perform its specific biochemical reaction. Without the cofactor, the protein portion of the holozyme, called the apoenzyme, is inactive. The complete, active enzyme, including both the apoenzyme and its cofactor, is referred to as the holoenzyme.

Cofactors can be broadly categorized into two types: metal ions and organic molecules. Metal ions, such as zinc, magnesium, or iron, can be directly involved in the catalytic mechanism by stabilizing transition states, acting as electron carriers, or facilitating substrate binding. Organic cofactors, often derived from vitamins, are also known as coenzymes. Examples include NAD+, FAD, and thiamine pyrophosphate. These coenzymes often act as temporary carriers of specific atoms or functional groups during enzymatic reactions. The nature of the cofactor and its interaction with the apoenzyme are critical for determining the enzyme's specificity and overall function within metabolic pathways. The binding of the cofactor to the apoenzyme can be reversible or irreversible, depending on the specific holozyme.