544 



THE BIOCHEMISTRY OF B VITAMINS 



Table 11. Specificity of the Configuration of Biotin. 



However, the racemic biotin is only half as active as the natural biotin 

 which is dextrorotatory. Synthetic ( + ) biotin is just as active as natural 

 biotin, whereas the synthetic ( — ) biotin is essentially inactive. The small 

 amount of activity which has been found is usually attributed to con- 

 tamination of the sample with traces of the dextrorotatory form. 



Kogl and co-workers 16 ~ 19 have concluded that two isomeric forms of 

 biotin exist in nature, a-biotin isolated from egg yolk and /3-biotin 

 isolated from liver by the procedure of du Vigneaud et al. 4 A mixture of 

 a-biotin (m. p. 220° C) and ^8-biotin (m. p. 232-3° C) melted at 197- 

 202° C; and a mixture of the methyl ester of a-biotin (m. p. 161-2° C) 

 and the methyl ester of /?-biotin (m. p. 163-4° C) showed a melting point 

 depression of 20-30° C. Specific rotations of the two biotins and their 

 methyl esters differed markedly. More significant was the isolation of a 

 sulfocaproic acid by hydrolysis of a-biotin to a diaminocarboxylic acid, 

 oxidation of the latter with lead tetracetate to an aldehyde, and finally 

 oxidation of the aldehyde with potassium permanganate in a series of 

 steps. This sulfocaproic acid, which was converted by alkali fusion to a 

 product identified as a, /?-dimethylbutyric acid, was found to be identical 

 with the synthetic ( — ) form of a-isopropyl-/?-sulfopropionic acid when 

 the melting points and mixed melting points of the anilides and m-tolu- 

 idine salts of each were studied. Since there is no branching in the carbon 

 skeleton of biotin, such a degradation product would indicate that another 

 structural form exists. 



Early work on the biological activity of the two biotins indicated that 

 /3-biotin was approximately twice as active as a-biotin for yeast, Rhizo- 



