Biotin

As long ago as 1898 it was shown that if dogs were fed raw egg white, diarrhea resulted. Following this it was shown that other mammals also suffered from egg white feeding, and that in addition to the diarrhea, skin ailments and nervous symptoms appeared. The phenomenon became known as egg white injury. Cooking the egg white prevented the injury. György proposed the term vitamin H for a factor which prevented egg white injury. Later, it was shown that this factor is identical with biotin, a vitamin known to be important for yeasts and microorganisms. The raw egg white unites with the biotin and prevents its utilization by mammals or birds.

Chemically, biotin is rather complicated. It has in its molecule a urea ring containing one sulfur atom; the ring is combined with a valeric acid group. The presence of sulfur in the molecule is not important for the vitamin activity, for if the sulfur is replaced by oxygen, the vitamin activity is retained. The formula of biotin is given below:

Biotin acts in extremely low concentration, and it is thus one of the most potent of the vitamins. Many organisms do not grow unless biotin is available for them. Usually in higher organisms it is synthesized in sufficient quantity, but biotin deficiency can occur naturally in birds and in insects. Lack of sufficient biotin has the same effect as egg white injury--diarrhea, disturbances in the skin and nervous system, in rats loss of hair about the eyes. It can also prevent the birth of young in rats. The protein in egg white which binds biotin is called avidin; it is a basic, carbohydrate-containing protein and it occurs not only in the eggs of birds but also in frog eggs.

There is now strong evidence that biotin is important in a process which is known as carbon dioxide fixation. Many bacteria, and higher organisms also, are able to utilize carbon dioxide and form organic compounds from it. This process is interfered with if biotin is lacking.