1. All enzymes are made up of proteins but all proteins are not enzymes.
2. Many enzymes are made up exclusively of protein and such enzymes are called simple enzymes.
3. In many enzymes, there is found a non-protein part associated with protein. Such enzymes are known as conjugated enzymes or holoenzymes.
4. The protein part of the conjugated enzyme is called apoenzyme.
5. The nonprotein part of the conjugated enzyme is called cofactor.
6. The co-factors are of three types:
- Prosthetic group
- Co-enzyme
- Activator
Conjugated enzyme or Holoenzyme = Apoenzyme + Co-factor
1. Prosthetic Group:
- When the non-protein part attached with the apoenzyme is an organic compound and is firmly bonded with the protein part, it is called a prosthetic group.
- The prosthetic group can not be separated from the protein part (the apoenzyme) without denaturation of the protein. Example: Cytochrome, Flavoprotein.
2. Co-enzyme:
- When the non-protein part is an organic compound and is only loosely attached with the protein part (the apoenzyme), it is called as co-enzyme.
- The co-enzyme can be easily separated from the protein part and can be easily attached again with it.
- Example: Co-enzyme A, NAD, FAD, NADP etc.
3. Activator:
- When the non-protein part is an inorganic substance such as some metal ion or mineral ion, it is called as an activator.
- The main role of the activator is to form a bond between the enzyme and the substrate molecule
- Example: K, Cu, Mn, Fe Zn, Ca etc
- As the proteins are colloidal in nature, they have large surface area per unit volume.
- The protein part of the enzyme contains one or more specific sites called active sites.
- During the enzymatic activity, the substrate molecules attach at these active sites.
- In the holoenzyme of the conjugated enzyme, the enzymatic activity is brought about by the holoenzyme.
- The apoenzyme alone or the nonprotein part alone can not act as an enzyme.
