Riboflavin becomes FAD and FMN
Vitamin B2 (riboflavin) is the raw material for two flavin coenzymes, flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN). Enzymes that use these are called flavoproteins, and they sit at the core of energy metabolism: complexes I and II of the electron transport chain depend on flavin coenzymes, as do the dehydrogenases of fatty acid oxidation and the citric acid cycle.
The diagram shows riboflavin feeding into FAD and FMN to power oxidative phosphorylation, capturing why a single vitamin underpins so much of cellular energy production.
Supporting roles and deficiency signs
Riboflavin's reach extends to recycling other nutrients: flavoproteins help regenerate the antioxidant glutathione and are needed to activate vitamin B6 and to convert folate, so a riboflavin shortfall can ripple into other B-vitamin pathways. Deficiency (ariboflavinosis) typically shows as cracks at the corners of the mouth, a sore tongue, and skin changes, and is more likely in poor diets or with malabsorption.
Riboflavin is generally safe and excess is excreted, often turning urine bright yellow. This is general educational information, not medical advice; suspected deficiency should be assessed by a qualified professional.