Vitamin B2 – Riboflavin

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Occurrence and structure

Riboflavin is also found in vegetable and animal products, especially in large quantities in milk and dairy products. Its structure is characterized by a tricyclic (consisting of three rings) isoalloxacin ring to which a ribitol residue is attached. Furthermore, vitamin B2 is in: broccoli, asparagus, spinach eggs and wholemeal products.


It occurs in FMN (flavin mononucleotide) and FAD (flavin adenine dinucleotide), which are important electron acceptors. This means that they can accept two protons (H+) and two electrons (e-), which are given off during a reaction because the reaction product no longer needs them. This looks like this: FAD à FADH2.

This reaction is called a hydrogenation (addition of hydrogen) and the resulting product is the above mentioned reduction equivalents, which then provide energy in the respiratory chain. About 1.5 ATP per FADH2. From the fact that FAD and FMN participate in reactions in which they are hydrogenated, it can be concluded that they are cofactors of reactions in which educts (starting materials) are dehydrated (i.e. electrons are withdrawn from them / hydrogen is withdrawn). For example, they are found in the following reactions/metabolic pathways

  • Beta-oxidation (breakdown of fatty acids, helper of acyl-CoA dehydrogenase)
  • Oxidative/dehydrogenating deamination (cleavage of amino groups)
  • Complex I of the respiratory chain (for the meaning of the respiratory chain see above)

Symptoms of deficiency

The symptoms of a lack of riboflavin (vitamin B2) are rather unspecific, since it occurs everywhere in the body. Occurrences can cause changes in the oral mucosa, among other things. Water-soluble (hydrophilic) vitamins: Fat-soluble (hydrophobic) vitamins:

  • Vitamin B1 – thiamine
  • Vitamin B2 – Riboflavin
  • Vitamin B3 – Niacin
  • Vitamin B5 – pantothenic acid
  • Vitamin B6 – PyridoxalPyridoxinPyridoxamine
  • Vitamin B7 – biotin
  • Vitamin B9 – folic acid
  • Vitamin B12 – cobalamin
  • Vitamin A – Retinol
  • Vitamin C – Ascorbic acid
  • Vitamin D – Calcitriol
  • Vitamin E – tocopherol
  • Vitamin K – PhylloquinoneMenachinone