Coenzymes are very important for carrying out different reactions taking place in our body. Coenzymes can be considered as helper molecules that help in chemical reactions. It acts as a catalyst to speed up the reaction. Coenzymes are complex organic compounds that are derived from vitamins and other essential nutrients required by our body in small amounts. Two coenzymes are crucial for various reactions, i.e., NAD and FAD.
NAD vs FAD
The main difference between NAD and FAD is that NAD can accept only one hydrogen atom, whereas FAD can accept two hydrogen atoms. NAD means Nicotinamide adenine dinucleotide, and FAD means Flavin adenine dinucleotide. Both have different roles to play, like NAD is a coenzyme that is found in all living beings, whereas FAD is a cofactor that helps in many metabolic and complex reactions.
NAD is Nicotinamide adenine dinucleotide which is a coenzyme very crucial for our metabolism. It is found in all the cells which are living. As the name dinucleotide suggests, it has two nucleotides that are joined together by phosphate groups. NAD can be found in two forms, i.e., oxidized and reduced form or state. It is also involved in other reactions, such as redox reactions which carry electrons from one end to another.
FAD is Flavin adenine dinucleotide is a cofactor which is the type of coenzyme, and it is involved in various enzymatic reactions that are necessary for metabolism. It belongs to the Flavin group, which, if it consists of protein, becomes flavoprotein and if flavin exists in another form, then becomes flavin mononucleotide. It has four redox states. It can either accept or donate an electron to become stable.
Comparison Table Between NAD and FAD
| Parameters of Comparison | NAD | FAD |
| Full form | NAD is Nicotinamide adenine dinucleotide. | FAD is Flavin adenine dinucleotide. |
| Definition | NAD is a coenzyme that can be found in living cells. | FAD is a redox cofactor involved in many metabolic and complex reactions. |
| Production | It is produced during glycolysis and the Krebs cycle. | It is only produced during the Krebs cycle. |
| Hydrogen | It accepts only one9 hydrogen atom. | It can accept two hydrogen atoms. |
| Electron Transfer | It transfers its electron to Cytochrome Complex 1 and gives 3 ATP. | It transfers its electron to Cytochrome Complex 2 and gives 2 ATP. |
What is NAD?
Nicotinamide adenine dinucleotide is also known by the name NAD consists of two nucleotides that are joined together by a phosphate group. It can exist in either an oxidized state, i.e., NAD+, or in a reduced state, i.e., NADH. Because its cofactor is found in two forms of cells, it acts as both oxidizing and reducing agents. This transfer of electrons from one place to another is the main function of NAD.
Two nucleotides are adenine nucleobase and nicotinamide. Apart from electron transfer, it also helps in the cellular process, such as acting as a catalyst or reagent of enzymes or adding and subtracting chemical groups from the protein itself. NAD and its enzymes are so important that it becomes very vital in drug discovery. Its chemical formula is C21H27N7O14P2.
It has a molar mass of 663.43g/molecule. Its melting point is 60 °C (320 °F; 433 K). It looks like a white powder whether it is in any state and is hygroscopic and water-soluble(highly) in nature. It can absorb ultraviolet lights because of the presence of adenine in it. It is not hazardous. It acts as a donor, messenger molecule to ADP ribose. It also acts as a substrate of DNA and other extracellular activities.
What is FAD?
Flavin adenine dinucleotide is also known by the name FAD, is very vital in the field of biochemistry. It is a redox-active coenzyme that is associated with different types of protein. It has four states in which it can exist: quinone, semiquinone,flavin-N(5)-oxide, and hydroquinone. In its oxidation state, FAD accepts two protons and two electrons to become FADH2.
Like NAD, FAD also has two parts which are adenine nucleotide, and the flavin mononucleotide (FMN) bonded together by phosphate groups. FAD can be reduced to form FADH2 by accepting two hydrogens and two electrons. Then FADH2 can be oxidized to form FADH by donating one hydrogen and one-electron atoms. Formation of FAD can be done by using various ways such as reduction, oxidation, and dehydration.
In different states, FAD has different colors. Like in a super oxidized state, it turns yellow-orange. In the fully oxidized state, it is yellow. In the half-reduced form, it is either red or blue-like pH, and if reduced fully, it becomes colorless. It has a chemical formula C27H33N9O15P2. It has a molar mass of 785.557 g/mol.
Main Differences Between NAD and FAD
- NAD is a Nicotinamide adenine dinucleotide consisting of adenine nucleobase, and nicotinamide joined via phosphate groups. FAD is a Flavin adenine dinucleotide consisting of a flavin group or flavin mononucleotide joined via phosphate groups.
- NAD is a coenzyme that can be found in living cells. FAD is a redox cofactor involved in many metabolic and complex reactions.
- NAD is reduced to NADH when produced during glycolysis and the Krebs cycles.FAD is reduced to FADH2 when produced only during the Krebs cycle.
- NAD accepts only one hydrogen atom. FAD can accept two hydrogen atoms.
- NAD transfers its electron to Cytochrome Complex 1 and gives 3 ATP for each NADH produced. FAD transfers its electron to Cytochrome Complex 2 and gives 2 ATP for each FDH2 produced.
Conclusion
Both NAD and FAD are actively involved in the process of cellular respiration. Both are derived from proteins and accept high-energy electrons and carry them to the electron transport chain. Both NAD and FAD are used to synthesize ATP molecules. NAD is derived from a compound named Niacin, also known as Vitamin B3. FAD is derived from a compound named Riboflavin, commonly known as Vitamin B2.
Both are coenzymes. NAD is very important for carrying and delivering hydrogen and electrons in the biochemical process, whereas FAD uses electrons and hydrogen to make ATP. Both are involved in the catabolic and anabolic processes through oxidation and reduction.
References
- https://pubs.acs.org/doi/abs/10.1021/bi002061f
- https://academic.oup.com/nar/article-abstract/31/3/e8/1130007