BIOTIN 



decarboxylation of oxaloacetic acid, however, by the observations of 

 Ochoa et al.,^ who isolated from pigeon and turkey livers an enzyme 

 that catalysed the reversible conversion of L-malic acid to pyruvic acid 

 plus carbon dioxide and the decarboxylation of oxaloacetic acid to 

 pyruvic acid. In biotin-deficient turkeys the amount of this enzyme, 

 though not of other enzymes catalysing related reactions was markedly 

 reduced but, unfortunately, the purified enzyme did not contain biotin. 



H. A. Lardy and his co-workers,^ however, have produced evidence 

 suggesting that biotin may be associated with carbon dioxide fixation 

 in several different enzyme reactions, not only in micro-organisms but 

 also in animals. Thus, in presence of biotin, L. arabinosus fixed C^* 

 from bicarbonate into cellular aspartic acid, but no fixation occurred 

 when the medium contained less than 0-05 m/xg. of biotin per ml., or 

 when aspartic acid or an anti-biotin was added. Again, C^* fixation 

 occurred to a greater extent in normal rats than in biotin-deficient 

 animals, and the livers of biotin-deficient animals synthesised citrul- 

 line at half the rate of normal or vitamin Bg-deficient animals ; the 

 rate was increased to normal by the intraperitoneal injection of biotin. 



Biotin containing C^^ was prepared by reacting the diamino- 

 carboxylic acid (page 407) with radioactive phosgene. When added to 

 cultures of L. arabinosus under conditions requiring its participation 

 in carbon dioxide fixation, there was no replacement of C^* by C^^, so 

 that the ureido carbonyl group is apparently not transferred during 

 carbon dioxide fixation. ^^ 



Deamination 



Carbon dioxide fixation does not appear to be the only function of 

 biotin and according to H. C. Lichstein and W. W. Umbreit,^^ it can 

 also restore the ability of E. colt to deaminate aspartic acid, serine 

 and threonine when this is lost by the cells having been left at pH 4 

 for thirty minutes at 27 to 37° C. Thus biotin appeared to be con- 

 nected with reaction {a) in the above scheme, as well as with reaction 

 {d). Similar results were obtained with other bacterial species, and 

 aspartic acid deaminase activity was restored by adenylic acid as well 

 as by biotin. In no instance was the alanine, phenylalanine, methio- 

 nine or glutamic acid deaminase activity affected by biotin, ^^ 



Axelrod et al.}^ however, failed to confirm these results, bat H. C. 

 Lichstein ^^ showed that this was due to their use of an unsuitable 

 medium. Adenylic acid was shown to be necessary for the activation 

 of biotin for the stimulation of cell-free aspartic acid deaminase, ^^ 

 and a deaminase activator that was neither biotin nor adenylic acid 

 was isolated from yeast by paper partition chromatography.^^ It 

 supported the growth of S. cerevisiae (Java strain) in a biotin-deficient 



444 



