From the Guidelines
FAD (Flavin Adenine Dinucleotide) is a coenzyme, not a cofactor. While these terms are sometimes used interchangeably, there is a technical distinction. FAD is specifically a coenzyme because it is an organic, non-protein molecule that binds to enzymes and helps them carry out their catalytic functions, as supported by the espen micronutrient guideline 1.
Key Points
- FAD is derived from riboflavin (vitamin B2) and plays a crucial role in redox reactions within cells, particularly in the electron transport chain during cellular respiration.
- It functions by accepting electrons and hydrogen atoms from substrates, converting between its oxidized form (FAD) and reduced form (FADH₂), which is essential for numerous metabolic processes including fatty acid oxidation, the citric acid cycle, and amino acid metabolism, as outlined in the espen micronutrient guideline 1.
- Unlike simple cofactors which are often inorganic ions, FAD has a complex organic structure and is temporarily bound to its associated enzymes during reactions, such as xanthine oxidase, succinic dehydrogenase, glutathione reductase, methylene-tetrahydrofolate reductase (MTHFR), and pyridoxine phosphate oxidase 1.
Clinical Implications
- The role of FAD in various metabolic processes highlights its importance in maintaining proper cellular function and overall health.
- Deficiencies in riboflavin, and subsequently FAD, can lead to impaired metabolic functions, emphasizing the need for a constant dietary supply of riboflavin, as it is not stored in the body in ample amounts 1.
From the Research
Definition of FAD
- FAD (Flavin Adenine Dinucleotide) is a redox-active coenzyme that regulates several important enzymatic reactions during metabolism 2.
- It is used in the medicinal and food industries, and FAD supplements have been used to treat some inheritable diseases 2.
Role of FAD in the Body
- FAD is a vital cofactor for a large number of flavoenzymes involved in energetic metabolism, protein folding, apoptosis, chromatin remodeling, and a number of other cell regulatory processes 3.
- The cellular and subcellular steady-state concentrations of flavin cofactors, including FAD, depend on carrier-mediated transport processes and on coordinated synthesizing/destroying enzymatic activities 3.
Biosynthesis of FAD
- FAD can be biosynthesized from flavin mononucleotide (FMN) and adenosine triphosphate (ATP), catalyzed by FAD synthetase (FADS) 2.
- The gene encoding FADS from the flavinogenic yeast Candida famata can be heterologously expressed in Escherichia coli for the biosynthesis of FAD 2.
Classification of FAD
- FAD is classified as a coenzyme, which is a non-protein organic compound that is required for the action of some enzymes 4.
- Coenzymes, including FAD, are essential for the catalytic activity of enzymes and play a crucial role in various metabolic processes 4.
Distinction between Cofactor and Coenzyme
- While the terms "cofactor" and "coenzyme" are often used interchangeably, a cofactor can be either a non-protein chemical compound or a metallic ion that is required for a enzyme's activity 4.
- FAD is more specifically classified as a coenzyme, which is a non-protein organic compound that is required for the action of some enzymes 4.