Functions: Riboflavin forms two coenzymes Flavin Mononucleotide (FMN) and Flavin Adenine Dinucleotide (FAD) . FMN and FAD serve as prosthetic groups of oxidoreductases. These enzymes are known as flavoproteins. Many flavoprotein enzymes contain one or more metals, e.g. molybdenum and iron, as essential cofactors and are known as metalloflavoproteins. Flavoproteins undergo reversible reduction of the isoalloxazine ring to yield the reduced forms FMNH2 and FADH2. Flavoprotein enzymes are widespread and are represented by several important oxidoreductases in metabolism,

Functions with the following enzymes

1. a-amino acid oxidase in amino acid deamination

2. xanthine oxidase in purine degradation

3. Aldehyde dehydrogenase in the degradation of aldehydes

4. Mitochondrial glycerol-3-phosphate dehydrogenase in transporting reducing equivalents

from the cytosol into mitochondria,

5. Succinate dehydrogenase in the Citric Acid Cycle,

6. Acyl-CoA dehydrogenase and the electron-transferring flavoprotein in fatty acid oxidation, and

7. In the oxidative decarboxylation of pyruvate and a-ketoglutarate by respective dehydrogenases.

8. FADH dehydrogenase is a major component of the respiratory chain in mitochondria. All of these enzyme systems are impaired in riboflavin deficiency.

Deficiency

A deficiency or riboflavin produces the following

Lips: A redness and shiny appearance of lips.

Cheilosis: Lesions at the mucocutaneous junction of mouth leading to painful fissures

Angular stomatitis: Seborrheic scaliness at the corners of the mouth, nose and nasolabial folds may occur.

Glossitis: The tongue assumes a red (magenta) colour

Eyes: Eyes may also become burning, develop corneal vascularisation and inflammation with cloudiness of cornea, photophobia and cataract.

RDA

 Infants :0.4-0.6mg

 Children :0.8-1.2mg

 Adult (male) :1.5-1.8mg

 Adult (female) :1.1-1.4mg

 Pregnant women :1.3-1.5mg

 Lactating women :1.6-1.9mg

Sources

Good sources : milk, liver, kidney, heart, fish

Fair sources : Cereals, roots, germinating wheat and barley