278 PYRIDOXINE AND RELATED COMPOUNDS 



a coenzyme for the synthesis of d- from L-alanine;^^^ this suggestion was 

 confirmed by the demonstration'"'^'' that cells of this organism (and many 

 other microorganisms) contain an enzyme capable of racemizing L-alanine, 

 and that pyridoxal phosphate is its coenzyme. Thus in the presence of 

 vitamin Be such cells synthesize D-alanine; in the absence of vitamin Be the 

 deficient cells will grow only if this essential D-amhio acid is supplied to 

 them. Deficient cells grown under the latter conditions contain the apo- 

 racemase but cannot racemize L-alanine for lack of pyridoxal phosphate.'^" 

 Cells of Streptococcus faecalis grown either with DL-alanine under the 

 above conditions or with low levels of vitamin Be have no detectable tyro- 

 sine decarboxylase activity, whereas when high levels of vitamin Be are 

 supplied the activity of this enzyme is high.''^' It was this finding with 

 vitamin Be-deficient bacteria which led to the identification of pyridoxal 

 phosphate as (1) the coenzymatic form of vitamin Be'^^ and (2) the coen- 

 zyme for the amino acid decarboxylases of both bacterial and mammalian 

 cells.i23.m 



When cells of S. faecalis are grown with DL-alanine replacing vitamin Be , 

 they are unable to carry out transamination between aspartic and keto- 

 giutaric acids, but they do so rapidly on addition of pyridoxal or pyridoxal 

 phosphate. ^^^ This une(iuivocal demonstration of the role of pyridoxal 

 phosphate as a coenzyme for the glutamic -aspartic transaminase not only 

 confirmed a role previously indicated for the vitamin'^^ ■ '" but showed that 

 greatly differing amounts of vitamin Be were required to activate different 

 vitamin Be-dependent reactions in the same cells. It had been observed 

 previously that cells of this organism grown with high levels of vitamin Be 

 carried out transamination and decarboxylation of tyrosine, whereas cells 

 grown with small amounts of the vitamin carried out transamination, but 

 not decarboxylation. '2^ 



Several reports'-^''^' have pointed out that lactic acid bacteria grown 

 with pyridoxine in the medium require certain amino acids for growth 

 that are no longer essential if the pyridoxine is replaced by pyridoxamine 



20 W. A. Wood and I. C. Gunsalus, /. Biol. Chem. 190, 403 (1951). 



21 W. D. Bellamy and I. C. Gunsalus, /. Bacteriol. 48, 191 (1944). 



22 I. C. Gunsalus and W. D. Bellamy, /. Biol. Chem. 155, 357 (1944). 



23 E. F. Gale, Advances in Enzijmol. 6, 1 (1946). 



24 E. Werle, Angew. Chem. 63, 550 (1951). 



25 H. C. Lichstein, I. C. Gunsalus, and W. W. Umbreit, /. Biol. Chem. 161, 311 (1945). 



26 E. E. Snell, /. Am. Chem. Sac. 67, 194 (1945). 



27 F. Schlenk and E. E. Snell, J. Biol. Chem. 157, 425 (1945). 



28 P. P. Cohen and H. C. Lichstein, J. Biol. Chem. 159, 367 (1945). 



29 M. L. Speck and D. A. Pitt, Science 106, 420 (1947). 



30 J. L. Stokes and M. Gunness, Science 101, 43 (1945). 



31 C. M. Lyman, O. Moseley, S. Wood, B. Butler, and F. Hale, ,/. Biol. Chem. 167, 

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