RIBOFLAVINE 



adenine dinucleotide on this organism. ^^ In the presence of alloxan, 

 however, the ribitylamino compound (II) was a potent stimulator of 

 L. helveticus. Both riboflavine phosphate and fiavine adenine diphos- 

 phate were as effective as riboflavine for growth and acid production 

 in L. helveticus. 



Fluorescyanine, in 50-/Ltg. doses, accelerated the growth of rats 

 maintained on a riboflavine-deficient diet, and abolished the nervous 

 symptoms from which the animals suffered.^* 



Growth Inhibitors 



Not all the analogues of riboflavine that fail to stimulate the 

 growth of organisms for which riboflavine is essential are merely inert 

 to the organisms, for some inhibit their growth. Thus, 6 : 7-dichloro- 

 9-D-i'-ribityl-isoalloxazine, which failed to stimulate the growth of 

 two strains of B. lactis acidi that were unable to grow without ribo- 

 flavine, and yeast. Staph, aureus and Streptobacterium plantarum, for 

 which riboflavine was not essential, inhibited the growth of all these 

 organisms with the exception of the yeast. ^^ Inhibition was com- 

 petitive, being overcome by the addition of riboflavine. The oxidation- 

 reduction potential of the antagonist was — 0-095 v. compared with 

 — 0-185 V. for riboflavine ; possibly the dichloro-compound is unable 

 to replace riboflavine because its dihydro-derivative is not sufficiently 

 negative to hydrogenate oxygen. Isoriboflavine ^^ (5 : 6-dimethyl-9- 

 D-i'-ribityl-isoalloxazine) counteracted the growth-promoting action 

 of riboflavine in rats, whilst the phenazine analogue of riboflavine i' 

 (2 : 4-diamino-7 : 8-dimethyl-io-ribityl-5 : lo-dihydrophenazine) 



CHa-(CHOH)3-CH20H 



CH3. ^ /N. /. .NH, 



CH 



NHi 



produced riboflavine deficiency in bacteria, and the dinitrophenazine 

 derivative from which it was prepared produced mild riboflavine 

 deficiency in mice. The effects of the compounds were overcome by 

 adequate amounts of riboflavine. Galactoflavine ^^ (6 : 7-dimethyl-9- 

 D-i'-dulcityl-isoalloxazine) inhibited the growth of rats receiving low 

 levels of riboflavine. Inhibition was competitive and was almost 

 completely counteracted by a daily intake of 200 fig. of riboflavine. 

 A similar, though less marked, effect was observed with D-arabo- 

 flavine ^^ in rats, but L-araboflavine had no such antagonistic effect. 



208 



