485 Pyridines 



i 

 CH2OH 



I 



HOOC C 



o II 



COOH 



CH 



CH3 



^NH" 



a-Hydroxymethyl-a'- 



(N-acetylaminomethylene)- 



succinic Acid 



Acid hydrolysis converts the acychc product to paraconic 

 acid. 



Functions of the vitamin are better understood. The 

 names pyridoxine or vitamin B^ commonly are used in a 

 general sense to refer to the group. Pyridoxal 5-phosphate 

 is the actual prosthetic group in most enzymic reactions. 

 It is a component of transaminases, amino acid decar- 

 boxylases, tryptophan synthetase, amino acid racemases, 

 threonine synthetase (homoserine isomerase), S-amino- 

 levulinate synthetase, phosphorylase and various other 

 enzymes which manipulate amino acids. More thorough 

 discussions of functions of this important vitamin can be 

 found in reviews. ^^' ^° 



Some pyridoxal-catalyzed reactions can be carried out in 

 aqueous solution without the apoenzymes if heat and the 

 proper metal ions (Al^"^*, Fe**, Cu++) are supplied. Mech- 

 anisms which have been proposed for three such reactions 

 are outhned in the following equations:-^' ^-- ^^- ^* 



^^ Esmond E. Snell, Vitamins and Hormones 16 77 (1958). 



-"Paul D. Boyer, Henry Lardy and Karl Myrback, (Eds.) "The 

 Enzymes," Alexander E. Braunstein, Pyridoxal phosphate, Academic 

 Press, New York, 1960, pp. 113-184. 



-^ David E. Metzler, Mlyoshi Ikawa and Esmond E. Snell, /. Am,. 

 Chem. Soc. 76 648 (1954). 



"J. B. Longenecker and Esmond E. Snell, ibid. 79 142 (1957). 



23 W. Terry Jenkins and Irwin W. Sizer, ibid. 79 2655 (1957). 



-* D. S. Hoare and Esmond E. Snell, Proc. Internat. Sympos. Enz. 

 Chem., Tokyo and Kyoto, Pergamon Press, London, 1957, p. 142. 



