BIOTIN 



References to Section 17 



1. G. Fraenkel and M. Blewett, Nature, 1942, 149, 301 ; 1942, 150, 



177 ; 1943. 151, 703- 



2. H. Rosenthal and T. Reichstein, ibid., 1942, 150, 546. 



3. G. Fraenkel and M. Blewett, Biochem. J., 1943, 37, 686. 



4. M. Blewett and G. Fraenkel, Proc. Roy. Soc. B., 1944, 132, 



212. 



5. L. Golberg, B. de Meillon and M, Lavoipierre, /. Exp. Biol., 1945, 



21, 90 ; W. Trager, /. Biol. Chem., 1949, 176, 121 1. 



6. G. Kitzes, H. A. Schuette and C. A. Elvehjem, /. Nutrition, 1943, 



26, 241. 



7. P. S. Sarma, Indian J. Med. Res., 1944, 32, 149. 



18. FUNCTION OF BIOTIN 



Miller et al.'^ sought to determine the function of biotin by esti- 

 mating the amounts present in a number of enzyme preparations, but 

 they failed to detect a single enzyme that contained more than one 

 molecule of biotin per molecule, and accordingly concluded that 

 biotin was only present as an impurity. D. Burk and R. J. Winzler 2 

 suggested that biotin was the prosthetic group of a coenzyme that 

 catalysed the transfer of carbon dioxide, whilst Koser et al.^ suggested 

 that it was concerned with the synthesis of aspartic acid, since the latter 

 stimulated the growth of Torula cremoris in the absence of biotin. 

 This was confirmed live years later, when Stokes ^ et at. showed that 

 S. faecalis R, L. helveticus and L. arabinosus failed to grow unless 

 about I m/Ag. of biotin and i mg. of aspartic acid per 10 ml. were 

 added to the medium but that if the biotin concentration were in- 

 creased to 10 m/xg. per 10 ml. the addition of aspartic acid was un- 

 necessary. Aspartic acid was therefore synthesised by organisms 

 grown in presence of excess biotin. Oxybiotin and the diaminocar- 

 boxylic acid (page 407) could replace biotin for this purpose, but 

 larger quantities were required. L. arabinosus was able to synthesise 

 aspartic acid from glutamic acid plus oxaloacetic acid, fumaric acid, 

 malic acid or succinic acid, and from alanine plus oxaloacetic acid, 

 but biotin did not play any part in these reactions. Apparently, 

 therefore, the enzyme system containing biotin was not concerned 

 with the final stage in the synthesis of aspartic acid, but with one of 

 the intermediate stages. 



Carboxylation and Decarboxylation 



Using E. colt, H. C. Lichstein and W. W. Umbreit ^ showed that 

 aspartic acid was degraded according to the following scheme : 



442 



