Main Difference – Prosthetic Group vs Coenzyme
Each cell possesses a unique set of biochemical reactions that define the identity of the cell. Enzymes are the biological catalysts that catalyze the biochemical reactions. Cofactors assist the function of the enzyme by binding to the inactive apoenzyme to produce the active holoenzyme. Cofactors can be either inorganic metal ions or small organic molecules. Prosthetic group and coenzyme are two types of cofactors. The main difference between prosthetic group and coenzyme is that prosthetic group can be either a metal or small organic molecule that is tightly bound to the enzyme structure either by covalent bond or non-covalent bond whereas coenzyme is a small organic molecule bound to the enzyme.
Key Areas Covered
1. What is a Prosthetic Group
– Definition, Facts, Examples
2. What is a Coenzyme
– Definition, Facts, Examples
3. What are the Similarities Between Prosthetic Group and Coenzyme
– Outline of Common Features
4. What is the Difference Between Prosthetic Group and Coenzyme
– Comparison of Key Differences
Key Terms: Coenzyme, Cofactor, Covalent Bonds, Enzyme, Metalloenzymes, Prosthetic Group
What is a Prosthetic Group
Prosthetic groups are a type of cofactors that bind tightly to enzymes or proteins. They are bound to the enzyme through covalent or non-covalent bonds. Some cofactors tightly bind to all types of enzymes. Others are tightly-bound to some enzymes while loosely-bound to other enzymes. Pyridoxal phosphate, flavin mononucleotide (FMN), flavin adenine dinucleotide (FAD), thiamin pyrophosphate (TPP), and biotin are examples of tightly bound organic compounds. Inorganic metal ions include Co, Mn, Mg, Cu, Fe, Zn. The enzymes that are tightly-bound with metal ions are known as metalloenzymes. A cofactor that binds to phenylalanine hydroxylase enzyme is shown in figure 1.
Figure 1: Cofactor
Prosthetic groups facilitate the binding and orientation of the substrate, formation of covalent bonds with the reaction intermediates, and interaction with a substrate to make it more electrophilic or nucleophilic.
What is a Coenzyme
Coenzymes are small organic molecules that bind to the enzymes, assisting the function of the enzyme. They serve as intermediate carriers of electrons, specific atoms or functional groups that are to be transferred during the catalyzing reaction. Most coenzymes are derived from the water-soluble B vitamins. NAD (nicotine adenine dinucleotide), NADP (nicotine adenine dinucleotide phosphate), FAD (flavin adenine dinucleotide) (Vit.B2), CoA (coenzyme A), CoQ (coenzyme Q), thiamine (vitamin B1), pyridoxine (vitamin B6), biotin, folic acid, etc. are the coenzymes that bind to the enzymes. Electrons, hydride ions, hydrogen atoms, methyl groups, oligosaccharides, and acyl groups are some of the chemical moieties transported by coenzymes. The transfer of electrons by NAD is shown in figure 2.
Figure 2: NAD Function
Coenzymes are modified during the reaction and another enzyme is required to restore the coenzyme to its original state. Since coenzymes are chemically changed during the reaction, they are considered as second substrates to the enzyme. Therefore, coenzymes are also called co-substrates. On the other hand, since coenzymes are regenerated in the body their concentrations should be maintained inside the body.
Similarities Between Prosthetic Group and Coenzyme
- Prosthetic group and coenzyme are two types of cofactors that assist the functioning of the enzyme.
- Both prosthetic group and coenzyme are non-protein part of the enzyme.
- Both prosthetic group and coenzyme can be small organic molecules.
Difference Between Prosthetic Group and Coenzyme
Definition
Prosthetic Group: Prosthetic groups are a type of cofactors that are tightly-bound to the enzymes or proteins.
Coenzyme: Cofactor is a non-protein chemical compound that is tightly and loosely bound to an enzyme or other protein molecules.
Type of Molecule
Prosthetic Group: Prosthetic groups can be either metal ions or small organic molecules.
Coenzyme: Coenzymes are small organic molecules.
Binding
Prosthetic Group: Prosthetic groups are tightly-bound or stably-associated with the enzyme.
Coenzyme: Coenzymes are loosely-bound to the enzyme.
Correspondence
Prosthetic Group: Either coenzymes or metal ions may serve as prosthetic groups.
Coenzyme: Coenzymes can be either tightly-bound (organic prosthetic groups) or loosely-bound small organic molecules.
Role
Prosthetic Group: Prosthetic group assists the functioning of the enzyme by binding with the apoenzyme.
Coenzyme: Coenzyme facilitates the biological transformation of the enzyme.
Removal
Prosthetic Group: Prosthetic groups are difficult to remove from the enzyme.
Coenzyme: Coenzymes can be easily removed from the enzyme.
Examples
Prosthetic Group: Metal ions such as Co, Mg, Cu, Fe and organic molecules such as biotin and FAD are examples of prosthetic groups.
Coenzyme: Coenzyme A, biotin, folic acid, vitamin B12, etc. are the examples of coenzymes.
Conclusion
Prosthetic group and coenzyme are two types of cofactors that assist the functioning of the enzymes. Prosthetic groups can be tightly-bound metal ions or simple organic molecules. Coenzymes are simple organic molecules. They can be either tightly or loosely-bound to the enzyme. The main difference between prosthetic group and coenzyme is the types of bonds between each type of cofactors.
Reference:
1. “Cofactors, Coenzymes and Prosthetic group.” Biochemistry for Medics – Lecture Notes, 22 June 2014, Available here.
Image Courtesy:
1. “Phenylalanine hydroxylase mutations” By Thomas Shafee – Own work (CC BY 4.0) via Commons Wikimedia
2. “Fermentation alcoolique” By Pancrat – Own work (CC BY-SA 3.0) via Commons Wikimedia
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