542 



BIOTIN 



7. a- AND jS-BlOTINS 



The chemical and physical characteristics of biotin isolated from liver 

 apply equally well for biotin obtained from milk and two other sources/^ 

 In contrast, Kogl and his coworkers^-'^^ have put forward the claim that 

 biotin exists in natural products in two chemically closely related forms 

 with comparable biological properties. Biotin originally obtained by Kogl 

 from egg yolk^- ^^ differed in melting point and specific rotation from biotin 



X(MU) 



Fig. 4. Ultraviolet absorption spectra of (1) the compound isolated from biotin; 

 (2) synthetic 5-(Q:-thienyl)valeric acid, in 95% alcohol. The wavelength is plotted 

 against the specific extinction. From D. B. Melville, Vitamins and Hormones 2, 62 

 (1944). 



isolated by Kogl from liver.''* Kogl further stated that a mixture of the 

 free acids and of their methyl esters from liver and egg yolk showed a 

 depression of melting point. X-ray analyses confirmed the non-identity 

 of the two substances. The compounds from egg yolk and liver were 



" D. B. Melville, Vitamins and Hormones 2, 66 (1944). 



« F. Kogl and W. A. J. Borg, Hoppe-Seyler's Z. physiol. Chem. 281, 65 (1944). 



« F. Kogl and E. J. ten Ham, Hoppe-Seyler's Z. physiol. Chem. 279, 140 (1943). 



■•* F. Kogl, H. Erxleben, and J. H. Verbeek, Hoppe-Seyler's Z. physiol. Chem. 276, 



63(1942). 

 " F. Kogl, J. H. Verbeek, H. Erxleben, and W. A. J. Borg, Hoppe-Seyler's Z. physiol. 



Chem. 279, 121 (1943). 

 ^6 F. Kogl, Ber. 68, 16 (1935). 



