678 THE BIOCHEMISTRY OF B VITAMINS 



Natural extracts also contain a substance (s) which inhibits growth of 

 the mutant. The toxicity is competitively prevented by riboflavin, but 

 the properties of the toxic material suggest that neither lumichrome nor 

 lumiflavin is responsible for the inhibitory activity of natural extracts. 53 



The growth of Lactobacillus casei stimulated by suboptimal amounts 

 of riboflavin is inhibited by high concentrations of lumiflavin; however, 

 in the presence of increased amounts of riboflavin, a stimulatory action 

 is exerted by the analogue. 31 Lumiflavin inhibits the utilization of flavin- 

 adenine-dinucleotide more effectively than the utilization of riboflavin 

 by the organism. 31 



2,4 - Diamino - 7,8 - dimethyl- 10(d,1' - ribityl) 5,10 - dihydrophenazine. The 

 growth of Lactobacillus casei in the presence of 0.03 y per cc of riboflavin 

 is completely inhibited by 200 y per cc of 2,4-diamino-7,8-dimethyl- 

 10(D,r-ribityl)5,10-dihydrophenazine. 54 The toxicity is prevented by 



2,4-diamino-7,8-dimethyl-l 0- (Z>, 1 '-ribityl) -5, 1 0-dihydrophenazine 



increasing the concentration of riboflavin to 100 y per cc. The inhibition 

 index appears to be approximately 6600. Half-maximum inhibition of 

 growth of Hemolytic streptococcus H69D and Lactobacillus arabinosus 

 resulted from addition of 330 y per cc of the diaminophenazine to a 

 medium containing 0.03 y per cc of riboflavin. Higher concentrations of 

 riboflavin prevent this inhibition of growth. Staphylococcus aureus, Strep- 

 tococcus faecalis R, and Escherichia coli are not affected in their growth 

 by the analogue. Because of the instability of the diaminophenazine, 

 reduction of the corresponding 2,4-dinitrophenazine with finely divided 

 iron in the culture medium is a desirable procedure. However, correspond- 

 ing results are obtained with purified diaminophenazine previously pre- 

 pared by reduction of the dinitrophenazine with tin. 54 



The dinitrophenazine produces in mice a very mild riboflavin deficiency 

 characterized by greasy, unkempt fur, by hyperirritability, and by a 

 slightly reduced rate of growth. Sufficient amounts of riboflavin prevent 

 the appearance of these changes. 



