Vitamin B2 (Riboflavin, Lactoflavin)

 Vitamin B₂ (Riboflavin, Lactoflavin)

Introduction

In 1932 Warburg and Christian were able to isolate yellow enzyme from yeast. The yellow enzyme was named riboflavin. In 1935 it was synthesized.

Chemistry

A flavin derivative riboflavin is a compound of D-ribitol (α-ribose alcohol) and a heterocyclic substance-isoalloxazine (flavin). The one-carbon of the ribityl group is attached at position 9 of isoalloxazine.

Properties

·        orange-yellow crystals

·        soluble in water to a limited degree

·        insoluble in fat-solvents

·        heat-stable in neutral and acid media

·        sensitive to light, unstable in alkaline solutions

·        stands ordinary cooking and canning

·        aqueous solutions are unstable to visible and ultra-violet light

·        produces a yellow solution having a yellow-green fluorescence

Distribution

Animal sources

·        Milk (Lactoflavin)

·        liver

·        kidney

·        muscle

·        eggs

Plant sources

·        Whole grain

·        green leafy vegetables

Functions

(1) Essential for growth.

(2) Both FMN and FAD in combination with protein (apoenzyme) play major role in a number of enzyme system and the enzyme containing this vitamin called flavoprotein. Riboflavin present in various enzyme systems in its two forms:

(a) In the form of riboflavin phosphate (FMN-flavin mononucleotide). FMN is a constituent of yellow enzyme of Warburg and Christian, cytochrome c reductase, L-amino acid dehydrogenase.

(b) In the form of FAD-flavin adenine dinucleotide. A great number of enzymes like xanthine oxidase, fumaric dehydrogenase, liver aldehyde oxidase, Haas enzymes, glycine oxidase, etc. contain FAD as prosthetic group.

(3) Riboflavin is related to the proteins metabolism.

(4) It is also the part of the prosthetic group of acyl-CoA dehydrogenase-the enzyme which mediates the first oxidative step in the oxidation of fatty acids.

Deficiency signs

The tissues which have originated from ectoderm (e.g., nervous system, skin, eyes) are first affected.

(1) Mouth

·        Cheilotic fissures at the corner of the mouth and ulcers on the lips

·        Angular stomatitis

·        Glossitis (magenta tongue).

(2) Eye

·        Keratitis,

·        corneal opacities,

·        vascularisation of cornea

·        Photophobia.

(3) Skin

·        Loss of hair

·        Dry and scaly skin.

(4) Arrested growth

Daily requirements

15 to 18 mg in adults i.e., 0.025 mg of riboflavin per 1 gm of protein..