559 



Pteridines and Flavines 



Adenine was found to be a more efficient precursor for 

 riboflavin than G-compound in C"-labeling studies,-^"^ and 

 guanine and xanthine have been found more efficient than 

 adenine. •' 



Acetate'" and shikimic acid" have been shown to be im- 

 probable direct precursors of the A ring of riboflavin. 

 Acetoin has been isolated from riboflavin fermentations*- 

 and is a normal metabolite of these organisms and of 

 other yeasts. On the basis of chemical studies this sub- 

 stance (or near derivatives) was proposed as a precursor 

 of the A ring of riboflavin.''^ '* It has been confirmed that 

 acetoin is an efficient biological precursor of the vitamin" 

 although intermediates cannot be ruled out entirely. 



At present, then, the following biosynthetic scheme 

 seems indicated: 



Purine, 



Purine nucleoside 



or 

 Purine nucleotide 



r^' 



3-^ R. Cresswell and H. Wood, Proc. Chem. Soc, 386 (1959). 



3»E. G. Brown, T. W. Goodwin and S. Pendleton, Biochem. J. 68 

 40 (1955). 



40 G. W. E. Plaut, ;. Biol. Chem. 211 111 (1954). 



"T. W. Goodwin and D. H. Treble, Biochem. J. 70 14 p (1958). 



42Toru Masuda, Pharm. Bull. (Japan) 5 136 (1957). 



«A. J. Birch and C. J. Moye, /. Chem. Soc, 412 (1957); 2622 

 (1958). 



