Riboflavin Vitamin B2 Vitamin G

Riboflavin is an orange crystalline substance, sparingly soluble in water, and markedly sensitive to light. The riboflavin molecule is complex. The structural formula follows:

The three rings represent an isoalloxazine constituent and this is combined with ribose, the pentose sugar also present in ribonucleic acids.

Although riboflavin is apparently a constituent of all or almost all types of protoplasm, many lower organisms do not require it in their food. Yeasts and molds have no need for it. Bacteria, in general, can get along without it. However, riboflavin serves as a growth factor for the tetanus bacillus, for lactic acid and propionic acid bacteria, and it is a requirement for Erysipelothrix rhusiopathiae and Listerella monocytogenes. The protozoan ciliates that have been investigated require riboflavin. So, too, do almost all the insects that have been studied. Riboflavin is essential for the growth and normal health of the rat, mouse, dog, pig, man, chicken and turkey. In riboflavin deficiency, various symptoms of ill health may appear. These include redness and roughness of the cornea of the eye, soreness at the corners of the lips, redness and soreness of the tongue, etc. At one time, it was thought that "ariboflavinosis," the disease caused by riboflavin deficiency, was extremely common. But the symptoms mentioned above are not always due to lack of riboflavin.

The presence of riboflavin in cells may be detected by fluorescence microscopy. Riboflavin is important for cell respiration. It and other alloxazine compounds combine with phosphoric acid and protein to form enzyme systems known as flavoproteins.