557 



Pteridines and Flayines 



with the incorporation of p-aminobenzoic acid into fohc 

 acid. Enzyme studies (E. coli extracts) now seem to have 

 narrowed this to inhibition of the couphng of the pteridine 

 moiety with p-aminobenzoic acid," although in the Myco- 

 bacterium avium study inhibition of peptide formation by 

 prevention of adenylo-p-aminobenzoic acid formation was 

 suggested. 



Investigation of the biosynthesis of riboflavin is facili- 

 tated by the existence of the two microorganisms, Eremo- 

 thecium ashbyii, a yeast, and Ashbya gossypii, a mold, 

 which are prodigious producers of this vitamin, evolving 

 large quantities into the culture medium. 



Besides riboflavin several other substances have been 

 isolated from riboflavin fermentations. The structures of 

 these metabolites suggest that they may be biosynthetic 

 precursors of the vitamin. 



CH3 



\ 



c=o 



I 

 CH-OH 



CH3 



HN 



NH2 



H NH., 



^V^ 



CH3 





CHs 



CH2— CH— CH— CH— CH2 



OH OH OH OH 



Acetoin 4,5-Diaminouracil 6,7-Dimethyl-8-(D- 1 '-ribityl)-lumazine 



G-Compound (green fluorescence) 



3HN 



OH OH OH OH 



6-Methyl-7-oxy-8-(D- 1 '-ribitylj-lumazine 

 V-Compound (violet fluorescence) 



OH OH OH OH 



Riboflavin 



They are shown in the accompanying formulas. 



Addition of purines to cultures of growing riboflavin 

 producers increases the yield of riboflavin.''- C"-8-Labeled 

 adenine contributes no radioactivity to the riboflavin mole- 



■'*i Gene M. Brown, Physiol. Revs. 40 359 (1960). 

 32 John A. MacLaren, /. Bacteriol. 63 233 (1952). 



