Cha pte r VII 



BIOTIN 



I. INTRODUCTION 



The discovery that certain strains of yeast would not grow on a 

 medium consisting solely of sugar and inorganic salts led E. Wildiers ^ 

 in 1901 to postulate the existence in yeast extracts and wort of a 

 substance necessary for the growth of certain yeasts. This hypo- 

 thetical substance he called " bios ". Yeasts were found to differ 

 greatly in their requirements for bios ; certain wild yeasts grew and 

 developed without it, whereas others showed no signs of growth in its 

 absence. 



The complex nature of bios was first recognised in 1922 by E. I. 

 Fulmer and V. E. Nelson, ^ who showed that it consisted of at least 

 two substances. Shortly afterwards W. Lash Miller ^ succeeded in 

 fractionating it into three substances all essential for growth. 



The first of these, which was termed Bios I, was shown by E. V. 

 Eastcott * to be meso-inositol. The second fraction. Bios IIa, was 

 identified by W. Lash Miller ^ as jS-alanine supplemented by L-leucine, 

 and by C. Rainbow and L. R. Bishop ® as pantothenic acid. The dis- 

 crepancy is explained by the fact that some yeasts require only 

 j3-alanine, whilst others require the whole pantothenic acid molecule. 



The third factor, Bios IIb, was shown to be identical with biotin, 

 isolated by F. Kogl and B. Tonnis ^ in the form of a crystalline methyl 

 ester from egg yolk. Other factors of the bios group were subse- 

 quently identified by Miller and his co-workers, and by Rainbow and 

 Bishop. These include aneurine, which appears to be identical with 

 the factor previously called Bios V,^ pyridoxine ^ and nicotinic acid.^^ 



In addition to being a growth factor for micro-organisms, biotin 

 was also recognised to be a vitamin, that is, a factor essential for the 

 growth of animals. In 1927, M. A. Boas-Fixsen ^^ observed that the 

 feeding of raw egg white to rats produced an eczema-like dermatitis 

 accompanied by loss of hair. She found that the condition was cured 

 by a " protective factor X " present in liver. What was apparently the 

 same factor was recognised by P. Gyorgy,^^ who called it vitamin H, 

 and subsequently showed ^^ that it possessed properties similar to those 

 of biotin prepared by Kogl and Tonnis from egg-yolk. 



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