553 



Pteridines and Flavines 



The synthesis of the labile methyl group of methionine 

 has been shown to involve a one-carbon unit at the form- 

 aldehyde oxidation level, and the "active formaldehyde" 

 form of the coenzyme has been implicated.'"' '■ Here, 

 again, not everything is known. The following route has 

 been suggested : ''• ^^ 



€' 





HOOC CH— CHo—CH.— S— CH, 



NH2 



OH OH 



S-Adenosylhomocysteine 



"Active 



Formaldehyde" 



Methionine 



Homo- 

 cysteine 



e 



00c— CH— CH2— CH2— S— CH. 



NH2 



OH OH 



S-Methylol-S-adenosylhomocysteine 



TPNH + H® 



G 



OOC— CH— CH,— CHo— S— CHs 



NH2 



OH OH 



S-Adenosylmethionine 



1" David Elwyn, Arthur Weissbach and David B. Sprinson, J. Am. 

 Chem. Soc. 73 5509 (1951). 



18 David B. Sprinson in W. D. McElroy and H. B. Glass (Editors), 

 "Amino Acid Metabolism," Johns Hopkins Press, Baltimore, 1955, p. 

 608. 



I'' Audrey Stevens and W. Takami, Federation Proc. 17 316 (1958). 



