RIBOFLAVIN 681 



rapid, reversible, and competitive, but the other is slower and apparently 

 irreversible. 02 



Quinine, atebrin, and a number of antimalarials prevent the growth of 

 Lactobacillus casein The inhibition is overcome to some extent, but 

 apparently not strictly competitively in most instances, by increasing 

 the riboflavin content of the medium. Thus, in media containing 0.25 y 

 and 2.5 y per cc of riboflavin, the maximum concentrations, respectively, 

 in mg per cc at which visible growth of Lactobacillus casei is observed 

 are 0.6 and 1.75 mg of quinine, 0.06 and 0.25 mg of atebrin, 0.02 and 0.1 

 mg of propamidine, 0.0034 and 0.01 mg of methylene blue, 0.29 and 1.22 

 mg of 2-p-chloroanilino-4-/3-diethylaminoethylamino-6-methylpyrimi- 

 dine, 63 0.42 and 2.5 mg of 2-p-chlorophenylguanidino-4-/?-diethylamino- 

 ethylamino-6-methylpyrimidine, 64 and 0.02 and 0.06 mg of 2-(6'-bromo- 

 B- naphthy lamino ) - 4 - diethylaminoethylamino - 6 - methy lpyrimidine. 55, 65 

 Other inhibitory substances not related to these compounds structurally 

 were not affected by additional riboflavin. 55 



NH— CH 2 — CH 2 — N(C 2 H 6 ) 2 



I 

 C 



°t) 



N CH 



I II 



C C— CH 3 



N N 



H 



2-p-chloroanilmo-4-^-diethyla7ni?ioethyla7nino-6-niethylpyrimidine 



CI— <r 



NH— CH 2 — CH 2 — N (C 2 H 5 ) 2 

 I 



C 

 ,/ \ 

 NH N C 



H I II 



C C C— CH 3 



./ \ / \ / 



N N N 



H H 



S-p-chlorophenylguanidino-4-^-diethylaminoethylamino-6-methylpyrimidine 



Atebrin has an inhibitory action on the tryptophanase activity of viable 

 cells of Escherichia coli but has little effect on the cell-free enzyme. The 

 inhibitory action of atebrin on the cells is reduced by addition of supple- 

 mentary riboflavin, and the effect has been attributed to the influence of 

 accumulated pyruvate on the system. 



Miscellaneous Analogues of Riboflavin. At concentrations of 25 y per 

 cc, 9-(D,r-sorbityl)isoalloxazine inhibits the growth of Bacillus lactis 



