Pharma gyan Pandit

Chemistry of Vitamin B2

Riboflavin is chemically known as 7,8-dimethyl-10 (1'-D-ribityl) isoalloxazine. In pure form it is a yelloworange, water-soluble compound. In tissues there is a broad distribution of flavin but little is present as free riboflavin. B2 is stable to heat, acid, and oxidation, however, destruction by light, especially ultraviolet light, as in sunlight. Thus, foods containing even moderate amounts of riboflavin, example, milk needs to be protected from sunlight. Only a little of the B2 in foods is lost in the cooking process.

In order to maintains the biological activity:

a)   positional 7 & 8 must be substrated with more than a hydrogen;

b)  The imine group in position 3 must be unsubstituted;

c)   A ribityl group on position 10

Fluorescence is pH dependent (best measuredbetween pH 4~8), maximal fluorescence occurs at 556 nm (yellow-green). The majority is found in flavocoenzymes [mainly in FAD and lesser amounts in FMN.

Flavocoenzymes are largely covalently associated within diverse flavoproteins.

a)   histidine & cysteinyl residue of succinate dehydrogenase [inner mitochondrial membrane]

b)  monoamine oxidase [outer mitochondrial membrane]

c)   L-gulonolactone oxidase [liver microsomes of animals], but some exist as 8α-linked FAD.