Apoenzymes are proteins that form active enzyme systems by combining with coenzymes and establishing system specificity for a substrate. Before entering this synthesis, it is often inactive; before joining with the coenzyme or cofactor, it is also known as a zymogen or proenzyme. In some cases, the original state contains a few extra amino acids that come out before it takes on its final structure as an apoenzyme.
An apoenzyme is just part of the structure of a larger enzyme. Enzyme activity is reliant on a specific chain of proteins. The cofactors, or coenzymes, are not always organic, but they generally come from a vitamin. However, a different type of cofactor is a metal ion activator. Inorganic, the metal ions often join with coordinate covalent bonds. The purpose behind the nutritional necessary for minerals is to give the body ions that create enzymes when combined with other polar atoms.
Apoenzymes form different types of associations with cofactors. Many cases feature loose bonds, and the two only come together when a reaction takes place. In other cases, covalent bonds hold them firmly together. The purpose of the cofactor is to change the protein to active status by altering its structure or by taking place in the reaction itself. The molecule that the enzyme acts on is the substrate.