Difference Between FAD and FMN

The key difference between FAD and FMN is that FAD molecule contains two nucleotide components, whereas FMN contains only one nucleotide component.

The term FAD stands for Flavin Adenine Dinucleotide while the term FMN stands for Flavin Mononucleotide. Both these are biomolecules that we can find in organisms. Moreover, they are the coenzyme forms of riboflavin.

1. Overview and Key Difference
2. What is FAD
3. What is FMN
4. Side by Side Comparison – FAD vs FMN in Tabular Form
5. Summary

What FAD?

The term FAD stands for Flavin Adenine Dinucleotide. It is a redox-active coenzyme that is associated with various proteins that are involved in several enzymatic reactions in metabolism. This compound falls under the category of flavoprotein. Flavoproteins are protein molecules that contain a flavin group, which can be in the form of FAD or FMN. Both FAD and FMN are tightly bound cofactors that can accept or donate two electrons and two protons to become fully reduced or donate or accept a single electron and a proton, forming the semiquinone intermediate.

Figure 01: Chemical Structure of FAD

The chemical formula of FAD is C₂₇H₃₃N₉O₁₅P₂. The molar mass of this compound is 785.557 mol/L. When extracted, this substance appears as white, vitreous crystals. There are two main portions in FAD molecule: an adenine nucleotide and a flavin mononucleotide. These two components are bridged together through the phosphate groups. In this molecule, the adenine component is attached to a cyclic ribose at the first carbon, and the phosphate group is attached to the ribose molecule at the fifth carbon atom.

Along with FMN, Fad can act as an enzyme cofactor. Both these are formed from riboflavin. Riboflavin is present in bacteria, fungi and plants because they can produce this molecule. However, eukaryotes such as humans cannot produce this substance, so we need to take it from outside. This is called Vitamin B2, and it is included in dietary sources.

What is FMN?

The term FMN stands for Flavin Mononucleotide. It is a biomolecule that forms from riboflavin (vitamin B2) through the act of an enzyme called riboflavin kinase. This substance can function as the prosthetic group of various oxidoreductases (such as NADH dehydrogenase). However, the name FMN is misleading because it is not truly a nucleotide since there is no glycosidic bond. Moreover, FMN is a stronger oxidizing agent compared to NAD, and this compound is important in both single and double electron transfers. FMN is the principal form of riboflavin we can find in cells and tissues. Our cells require more energy to produce this compound, but it is a soluble component compared to riboflavin (the parent molecule).

Figure 02: Structure of FMN

FMN is used as a food additive due to its ability to provide an orange-red food colour. The designation for this food colouring is E number E101a. The sodium salt of FMN has the E number E 106 and it a very closely related food dye. This sodium salt easily and rapidly turns into free riboflavin after ingestion. Therefore, we can find these food additives in foods for babies, jams, milk products, and sweet products.

What is the Difference Between FAD and FMN?

FAD stands for Flavin Adenine Dinucleotide while FMN stands for Flavin Mononucleotide. The key difference between FAD and FMN is that FAD molecule contains two nucleotide components, whereas FMN contains only one nucleotide component. Concerning the applications, the FAD is mainly useful as a cofactor in cells and tissues. But, FMN is mainly useful as a food additive in milk products, sweets, baby food, for orange-red colouration.

Below infographic shows the differences between FAD and FMN in tabular form.

Summary – FAD vs FMN

FAD and FMN are biomolecules we can find in biological organisms. The key difference between FAD and FMN is that FAD molecule contains two nucleotide components, whereas FMN contains only one nucleotide component.

Reference:

1. “Flavin mononucleotide.” Pubchem, Available here.

Image Courtesy:

1. “FAD” By UMcrc14 – Own work (Public Domain) via Commons Wikimedia
2. “Flavin mononucleotide” By Edgar181 – Own work (Public Domain) via Commons Wikimedia