242 PYRIDOXINE AND RELATED COMPOUNDS 



Although such a postulate is a possibility, there seems to l)e no positive evi- 

 dence for it and in the case of the transaminases there is some evidence 

 against it.'^^ 



D. ANTAGONISTS 



Only one of the vitamin Be antagonists, desoxypyridoxine, has been 

 studied by enzymatic techniques.'" This material acts by being itself phos- 

 phorylated and competing, in the form of desoxypyridoxine phosphate, 

 with pyridoxal phosphate for the surface of the apoenzyme. 



VI. Biogenesis 



W. W. UMBREIT 



The origin of the vitamin Be molecule is not known. The transformations 

 among the various members of the vitamin Be group are outlined on p. 241. 

 The original hypothesis of SnelP that, since D-alanine replaced the growth 

 requirement of certain bacteria for vitamin Be , condensation between d- 

 alanine and a 4-carbon dicarboxy acid might serve to form pyridoxal has 

 not been borne out by subsequent data, since organisms grown on D-alanine 

 do not contain vitamin Be . There appears to be a requirement for D-alanine- 

 which in the presence of vitamin Be is met from L-alanine and the pyridoxal 

 phosphate containing racemase.'^ 



VII. Estimation 



HENRY SHERMAN 



Since many of the compounds which possess vitamin Be activity occur in 

 nature as conjugates which are, in large part, firmly bound to tissue, pre- 



31 E. F. Gale, Advances in Enzymol. 6, 1 (1946). 



32 I. C. Gunsalus, Federation Proc. 9, 556 (1950). 



33 O. Schales, Advances in Enzymol. 7, 513 (1947). 



3'' O. Schales, in The Enzymes, Vol. 2, Part 1, p. 216. Academic Press, New York, 



1951. 

 3^ E. Werle, Z. Vitamin- Harmon u. Fermentforsch. 1, 504 (1947). 



36 P. P. Cohen, in The Enzymes, Vol. 1, Part 2, p. 1040. Academic Press, New ^Ork. 

 1951. 



37 F. Schlenk and E. E. Snell, ./. Biul. Chan. 157, 425 (1945). 



38 F. Schlenk and A. Fisher, Arch. Biochem. 8, 337 (1945). 



39 E. Werle and W. Koch, Biochem. Z. 319, 305 (1949). 



1 E. E. Snell and B. M. Girard, Proc. Natl. Acad. Sci. 29, 66 (1943). 



2 E. E. Snell, J. Biol. Chem. 158, 497 (1945). 



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



