Flavin mononucleotide (FMN) is a molecule found in nearly all living organisms, playing a fundamental part in numerous biological processes. It contributes to various bodily functions, including the metabolism of carbohydrates, fats, and proteins.
What is Flavin Mononucleotide?
Flavin mononucleotide (FMN), also known as riboflavin-5′-phosphate, is a biomolecule derived from riboflavin (Vitamin B2). The conversion of riboflavin to FMN occurs through the action of an enzyme called riboflavin kinase. FMN functions as a coenzyme, a non-protein compound that assists enzymes in carrying out their specific tasks within the body.
FMN’s chemical structure consists of a flavin group, a ribose sugar, and a phosphate group. The flavin component, specifically its isoalloxazine ring, is important for its coenzymatic activity. It is the primary form in which riboflavin is found within human cells and tissues.
FMN’s Role in Cellular Processes
Flavin mononucleotide (FMN) plays a role in the body’s energy production. It functions as an electron carrier in redox reactions, processes involving the transfer of electrons between molecules. These reactions are fundamental for converting food into usable energy in the form of adenosine triphosphate (ATP).
FMN is an integral component of the electron transport chain (ETC), located within the inner mitochondrial membrane. FMN facilitates the transfer of electrons from NADH to Complex I of the ETC. This electron transfer is a part of oxidative phosphorylation, the process that drives ATP generation. FMN also participates in other metabolic pathways, such as fatty acid metabolism.
Obtaining FMN Through Diet
Humans acquire flavin mononucleotide (FMN) primarily through the dietary intake of riboflavin (Vitamin B2). More than 90% of the riboflavin consumed is in the form of FMN or flavin adenine dinucleotide (FAD). Common food sources rich in riboflavin include:
- Dairy products like milk and cheese
- Various meats
- Eggs
- Leafy green vegetables such as spinach and kale
- Fortified cereals
- Whole grains
Once ingested, riboflavin is absorbed mainly in the proximal small intestine as free riboflavin. Enzymes in the intestinal lumen assist in this absorption process. After absorption, riboflavin is converted into its coenzyme forms, including FMN, within the body’s cells by enzymes. Riboflavin, and thus FMN, is sensitive to light and can be inactivated by ultraviolet and visible light. This is why milk, a good source of riboflavin, is now packaged in opaque containers rather than clear glass bottles.
Recognizing FMN Deficiency
Insufficient levels of flavin mononucleotide (FMN), stemming from riboflavin deficiency, can lead to ariboflavinosis. Symptoms often manifest in the mucous membranes, skin, and eyes. Common signs include cracked lips (cheilosis) and inflammation at the corners of the mouth (angular stomatitis).
The tongue may become inflamed and red (glossitis). Skin disorders, such as seborrheic dermatitis, with red and itchy patches, can also occur. Eye-related symptoms include redness, irritation, and increased sensitivity to light. Populations at higher risk for riboflavin deficiency include vegans, pregnant and lactating women, and individuals with gastrointestinal disorders that impair nutrient absorption. Severe and prolonged deficiency can also contribute to anemia and, in some cases, cataracts.