Vitamin B2 or Riboflavin – Chemistry, Sources, Daily Requirement, Biochemical Functions And Deficiency Symptoms

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Vitamin B2 is also known as Riboflavin. It is very much essential for a variety of cellular oxidation and reduction reactions.

Flavin mono nucleotide FMN and Flavin adenine dinucleotide FAD are the coenzymes of riboflavin.


Riboflavin contains 6, 7- dimethyl iso alloxaxine (a hetero cyclic 3 ring structure) attached to D- ribitol by a nitrogen atom. Ribitol is a open chain form of sugar ribose with aldehyde group CHO reduced to alcohol(CH2OH).

Riboflavin is stable to heat but sensitive to light. When exposed to ultra violet rays of sun light it exhibits yellow fluorescence because of the conversion of riboflavin to lumiflavin.

Some substances which were originally thought to be different are structurally identical to riboflavin.

They are

·Lactoflavin of milk

·Hepatoflavin from liver

·Ovoflavin from egg.

Biochemical functions:

The flavin enzymes and coenzymes like FAD and FMN participate in many Redox reactions responsible forenergy production. The functional unit of both the coenzymes is the iso alloxazine ring which serves as a receptor of two hydrogen atom (with electrons). Both undergo identical reversible reaction to form FADH2 and FMNH2.

The enzymes which use flavin coenzymes are called flavo proteins. These coenzymes are bound by either non covalent or covalent bonds to form the holo enzyme. Many flavor proteins contain metal atoms like iron and cadmium. Hence they are known as metallo flavo proteins.

The coenzymes FAD and FMN are associated with certain enzymes involved in carbohydrate metabolism, lipid metabolism, purine and pyramidine metabolism. They are also essential for active electron transport chain

Recommended dietary allowance: RDA

The daily requirement of riboflavin for an adult is1.2 – 1.7 mg. Higher quantities are advised in pregnancy and lactation.

Dietary sources

Milk and milk products

Meat, liver and kidney

Fish andEggs


Fruits and vegetables

Deficiency symptoms:

Riboflavin deficiency symptoms include cheilosis which causes fissures at the corners or angles of mouth, glossitis with smooth and purplish tongue and also dermatitis.

But riboflavin deficiency is uncommon. It is mostly found along with other vitamin deficiency syndromes.

Chronic alcoholics are susceptible to B2 deficiency. Assay of the enzyme gluta thione reductase in erythrocytes will be useful in assessing riboflavin deficiency.


Galacto flavin is the anti metabolite of riboflavin.


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