FAD Full Form

Fad stands for Flavin Adenine Dinucleotide, a biomolecule derived from riboflavin (vitamin B2). It is the coenzyme form of vitamin B2 used in clinical conditions of vitamin B2 deficiency. It is one of the forms of flavoprotein and another form is flavin mononucleotide (FMN for short).

It can exist in four particular redox statesstates, which are the flavin-N(5)-oxide, quinone, semiquinone, and hydroquinone. FAD is transformed between these states by gaining or losing electrons. FAD, in its fully oxidized or quinone form, receives two electrons and two protons, becoming FADH2 (hydroquinone form). Semiquinones (FADH.) can be formed either by the reduction of FAD or the oxidation of FADH2 by the gain or loss of electrons or protons, respectively. However, some proteins generate and maintain super oxidised forms of the flavin cofactor, flavin N(5)-oxide.

Composition of FAD

• Chemical formula of Flavin Adenine Dinucleotide is C27H33N9O15P2
• Has a molar mass of 785.557 g·mol−1
• It makes a white and vitreous appearance in the form of crystals
• Also known as riboflavin 5′-adenosine diphosphate
• Its IUPAC name is – ({(2R,3S,4R,5R)-5-(6-amino-9H-purin-9-yl)-3,4-dihydroxy oxolan-2-yl methoxy}(hydroxy)phosphoryl)oxy({(2R,3S,4S)-5-{7,8-dimethyl-2,4-dioxo-2H,3H,4H,10H-benzogpteridin-10-yl}-2,3,4-trihydroxy pentyloxy})phosphinic acid.

Exists in four redox states given as:

1. Flavin N(5)-oxide: super oxidized
2. quinone form (FAD): fully oxidised
3. hydroquinone form (FADH2): formed when the quinone form of FAD accepts two electrons and two protons to form FADH2.
4. semiquinone form (FADH): H produced by either reduction of FAD or oxidation of FADH2. It is a nucleotide composed of a nucleobase, a pentose, and a phosphate group.
5. It is autofluorescent and consists of an isoalloxazine ring connected to a ribityl adenine diphosphate.

Properties of states of FAD

FAD – Quinone form – it is fully oxidized, is yellow in color, and has an aromatic ring system

FADH – Semiquinone form – it is half reduced is blue or red in color, and is unstable in aqueous solution

FADH₂ – Hydroquinone form – it is fully reduced: has no color, and has high polarizability, higher energy

flavin-N(5)-oxide: Superoxidised: yellow-orange in color

Processes that depend on FAD:

• Metabolism
• Bioenergetics
• Protein folding
• ROS production
• Defence against oxidative stress
• Redox epigenetics
• Cell differentiation

Involvement in Metabolism Pathways

• Glutathione Metabolism: This pathway involves the production of the antioxidant glutathione, which plays a key role in regulating antioxidant defense, nutrient metabolism, and cellular events.

• Caffeine Metabolism: This pathway is primarily involved in the metabolism of caffeine to paraxanthine (also known as 1,7-dimethylxanthine) via N-3-demethylation.

• Valine, Leucine, and Isoleucine Breakdown: The breakdown of all three essential amino acids, valine, leucine, and isoleucine, begins in muscle to produce NADH and FADH₂, which can be used to generate ATP.

• Lysine degradation: a mitochondrial-restricted pathway that proceeds through the formation of saccharopine.

• Folate Metabolism: It is the production of folic acid that is essential for the synthesis of DNA, modification of DNA and RNA, and various other chemical reactions involved in cell metabolism.

• Riboflavin metabolism:I t occurs in enterocytes where riboflavin is metabolized to flavin mononucleotide (FMN) by riboflavin kinase (RFK) or to flavin adenine dinucleotide (FAD) by FAD synthase (FADS).

Significance of FAD

• Disorders associated with flavoproteins: Riboflavin deficiency (and consequent FAD and FMN deficiency) can lead to health problems. For example, ALS patients have decreased levels of FAD synthesis.

• Drug Design: In antibacterial drug development, metabolic proteins that utilize FAD (complex II) are important for bacterial virulence.

• Optogenetics: Targeting FAD synthesis or the production of FAD analogs may therefore be a useful area of investigation. It is a process that allows many new tools, such as the blue-light-utilizing FAD domain (BLUF), to make great strides.

• Treatment Monitoring: The natural fluorescence of FAD allows scientists to monitor disease progression, and treatment efficacy, and aid in the diagnosis of various cases such as invasive oral cancer.